Add type annotations and use C-level objects instead of py-ones where it
is easy to do. We are not all-good yet, but this already brings some noticable speedup:

    name                 old time/op  new time/op  delta
    quote[a]              786µs ± 1%    10µs ± 0%  -98.76%  (p=0.016 n=4+5)
    quote[\u03b1]        1.12ms ± 0%  0.41ms ± 0%  -63.37%  (p=0.008 n=5+5)
    quote[\u65e5]         738µs ± 2%   258µs ± 0%  -65.07%  (p=0.016 n=4+5)
    quote[\U0001f64f]     920µs ± 1%    78µs ± 0%  -91.46%  (p=0.016 n=5+4)
    stdquote             1.19µs ± 0%  1.19µs ± 0%     ~     (p=0.794 n=5+5)
    unquote[a]           1.08ms ± 0%  1.08ms ± 1%     ~     (p=0.548 n=5+5)
    unquote[\u03b1]       797µs ± 0%   807µs ± 1%   +1.23%  (p=0.008 n=5+5)
    unquote[\u65e5]       522µs ± 0%   520µs ± 1%     ~     (p=0.056 n=5+5)
    unquote[\U0001f64f]  3.21ms ± 0%  3.14ms ± 0%   -2.13%  (p=0.008 n=5+5)
    stdunquote            815ns ± 0%   836ns ± 0%   +2.63%  (p=0.008 n=5+5)

Since 50b8cb7e (strconv: Move functionality related to UTF8
encode/decode into _golang_str) both golang_str and strconv import each
other.

Before this patch that import was done at py level at runtime from
outside to workaround the import cycle. This results in that strconv
functionality is not available while golang is only being imported.
So far it was not a problem, but when builtin string types will become
patched with bstr and ustr, that will become a problem because string
repr starts to be used at import time, which for pybstr is implemented
via strconv.quote .

-> Fix this by switching golang and strconv to cimport each other at pyx
level. There, similarly to C, the cycle works just ok out of the box.

This also automatically helps performance a bit:

    name                 old time/op  new time/op  delta
    quote[a]              805µs ± 0%   786µs ± 1%   -2.40%  (p=0.016 n=5+4)
    quote[\u03b1]        1.21ms ± 0%  1.12ms ± 0%   -7.47%  (p=0.008 n=5+5)
    quote[\u65e5]         785µs ± 0%   738µs ± 2%   -5.97%  (p=0.016 n=5+4)
    quote[\U0001f64f]    1.04ms ± 0%  0.92ms ± 1%  -11.73%  (p=0.008 n=5+5)
    stdquote             1.18µs ± 0%  1.19µs ± 0%   +0.54%  (p=0.008 n=5+5)
    unquote[a]           1.26ms ± 0%  1.08ms ± 0%  -14.66%  (p=0.008 n=5+5)
    unquote[\u03b1]       911µs ± 1%   797µs ± 0%  -12.55%  (p=0.008 n=5+5)
    unquote[\u65e5]       592µs ± 0%   522µs ± 0%  -11.81%  (p=0.008 n=5+5)
    unquote[\U0001f64f]  3.46ms ± 0%  3.21ms ± 0%   -7.34%  (p=0.008 n=5+5)
    stdunquote            812ns ± 1%   815ns ± 0%     ~     (p=0.183 n=5+5)

So far this is plain code movement with no type annotations added and
internal from-strconv imports still being done via py level.

As expected this does not help practically for performance yet:

    name                 old time/op  new time/op  delta
    quote[a]              910µs ± 0%   805µs ± 0%  -11.54%  (p=0.008 n=5+5)
    quote[\u03b1]        1.23ms ± 0%  1.21ms ± 0%   -1.24%  (p=0.008 n=5+5)
    quote[\u65e5]         800µs ± 0%   785µs ± 0%   -1.86%  (p=0.016 n=4+5)
    quote[\U0001f64f]    1.06ms ± 1%  1.04ms ± 0%   -1.92%  (p=0.008 n=5+5)
    stdquote             1.17µs ± 0%  1.18µs ± 0%   +0.80%  (p=0.008 n=5+5)
    unquote[a]           1.33ms ± 1%  1.26ms ± 0%   -5.13%  (p=0.008 n=5+5)
    unquote[\u03b1]       952µs ± 2%   911µs ± 1%   -4.25%  (p=0.008 n=5+5)
    unquote[\u65e5]       613µs ± 2%   592µs ± 0%   -3.48%  (p=0.008 n=5+5)
    unquote[\U0001f64f]  3.62ms ± 1%  3.46ms ± 0%   -4.32%  (p=0.008 n=5+5)
    stdunquote            788ns ± 0%   812ns ± 1%   +3.07%  (p=0.016 n=4+5)

We will soon need to use error rune codepoint from both golang_str.pyx
and strconv.pyx - so we need to move that definition into shared place.
What fits best is unicode/utf8, so start that package and move the
constant there.

We added byte and rune types in the previous patch. Let's use them now
throughout whole codebase where appropriate.

Currently the only place where unicode-codepoint is used is
_utf8_decode_rune. uint8_t was used in many places.

Those types are the base when working with byte- and unicode strings.
It will be clearer to use them explicitly instead of uint8_t and int32_t
when processing string.

This functions are currently relatively slow. They were initially used
in zodbdump and zodbrestore, where their speed did not matter much, but
with bstr and ustr, since e.g. quote is used in repr, not having them to
perform with speed similar to builtin string escaping starts to be an
issue. Tatuya Kamada reports at nexedi/pygolang!21 (comment 170833) :

    ### 3. `u` seems slow with large arrays especially when `repr` it

    I have faced a slowness while testing `u`, `b` with python 2.7, especially with `repr`.

    ```python
    >>> timeit.timeit("from golang import b,u; u('あ'*199998)", number=10)
    2.02020001411438
    >>> timeit.timeit("from golang import b,u; repr(u('あ'*199998))", number=10)
    54.60263395309448
    ```

    `bytes`(str) is very fast.

    ```python
    >>> timeit.timeit("from golang import b,u; bytes('あ'*199998)", number=10)
    0.000392913818359375
    >>> timeit.timeit("from golang import b,u; repr(bytes('あ'*199998))", number=10)
    0.4604980945587158
    ```

    `b` is much faster than `u`, but still the repr seems slow.

    ```
    >>> timeit.timeit("from golang import b,u; b('あ'*199998)", number=10)
    0.0009968280792236328
    >>> timeit.timeit("from golang import b,u; repr(b('あ'*199998))", number=10)
    25.498882055282593
    ```

The "repr" part of this problem is due to that both bstr.__repr__ and
ustr.__repr__ use custom quoting routines which currently are implemented in
pure python in strconv module:

https://lab.nexedi.com/kirr/pygolang/blob/300d7dfa/golang/_golang_str.pyx#L282-291
https://lab.nexedi.com/kirr/pygolang/blob/300d7dfa/golang/_golang_str.pyx#L582-591
https://lab.nexedi.com/kirr/pygolang/blob/300d7dfa/golang/_golang_str.pyx#L941-970
https://lab.nexedi.com/kirr/pygolang/blob/300d7dfa/golang/strconv.py#L31-92

The fix would be to move strconv.py to Cython and to correspondingly rework it
to avoid using python-level constructs during quoting internally.

Working on that was not a priority, but soon I will need to move strconv to
Cython for another reason: to be able to break import cycle in between _golang
and strconv.

So it makes sense to add strconv benchmark first - since we'll start moving it
to Cython anyway - to see where we are and how further changes will help
performance-wise.

Currently we are at

    name                 time/op
    quote[a]              910µs ± 0%
    quote[\u03b1]        1.23ms ± 0%
    quote[\u65e5]         800µs ± 0%
    quote[\U0001f64f]    1.06ms ± 1%
    stdquote             1.17µs ± 0%
    unquote[a]           1.33ms ± 1%
    unquote[\u03b1]       952µs ± 2%
    unquote[\u65e5]       613µs ± 2%
    unquote[\U0001f64f]  3.62ms ± 1%
    stdunquote            788ns ± 0%

i.e. on py2 quoting is ~ 1000x slower than builtin string escaping, and unquoting is
even slower.

on py3 the situation is better, but still not good:

    name                 time/op
    quote[a]              579µs ± 1%
    quote[\u03b1]         942µs ± 1%
    quote[\u65e5]         595µs ± 0%
    quote[\U0001f64f]     274µs ± 1%
    stdquote             2.70µs ± 0%
    unquote[a]            696µs ± 1%
    unquote[\u03b1]       763µs ± 0%
    unquote[\u65e5]       474µs ± 1%
    unquote[\U0001f64f]   187µs ± 0%
    stdunquote            808ns ± 0%

δ(py2, py3) for the reference:

    name                 py2 time/op  py3 time/op  delta
    quote[a]              910µs ± 0%   579µs ± 1%   -36.42%  (p=0.008 n=5+5)
    quote[\u03b1]        1.23ms ± 0%  0.94ms ± 1%   -23.17%  (p=0.008 n=5+5)
    quote[\u65e5]         800µs ± 0%   595µs ± 0%   -25.63%  (p=0.016 n=4+5)
    quote[\U0001f64f]    1.06ms ± 1%  0.27ms ± 1%   -74.23%  (p=0.008 n=5+5)
    stdquote             1.17µs ± 0%  2.70µs ± 0%  +129.71%  (p=0.008 n=5+5)
    unquote[a]           1.33ms ± 1%  0.70ms ± 1%   -47.71%  (p=0.008 n=5+5)
    unquote[\u03b1]       952µs ± 2%   763µs ± 0%   -19.82%  (p=0.008 n=5+5)
    unquote[\u65e5]       613µs ± 2%   474µs ± 1%   -22.76%  (p=0.008 n=5+5)
    unquote[\U0001f64f]  3.62ms ± 1%  0.19ms ± 0%   -94.84%  (p=0.016 n=5+4)
    stdunquote            788ns ± 0%   808ns ± 0%    +2.59%  (p=0.016 n=4+5)

And let pybstr/pyustr point to version of bstr/ustr types that is actually in use:
- when bytes/unicode are not patched -> to _pybstr/_pyustr
- when bytes/unicode will be patched -> to bytes/unicode to where original
  _pybstr/_pyustr were copied during bytes/unicode patching.
at runtime the code uses pybstr/pyustr instead of _pybstr/_pyustr.

GPython will patch builtin bytes and unicode types.
zbytes and zunicode will refer to original unpatched types.
We will use them to invoke original bytes/unicode methods.

NOTE we will test against bytes/unicode - not zbytes/zunicode - when
inspecting type of objects. In other words we will use original
bytes/unicode types only to refer to their original methods and code.

For gpython to switch builtin str/unicode to bstr/ustr we will need
bstr/ustr to have exactly the same C layout as builtin string types.
This is possible to achieve only via `cdef class`. It is also good to
switch to `cdef class` for RAM savings - from https://github.com/cython/cython/pull/5212#issuecomment-1387659026 :

    # what Cython does at runtime for `class MyBytes(bytes)`
    In [3]: MyBytes = type('MyBytes', (bytes,), {'__slots__': ()})

    In [4]: MyBytes
    Out[4]: __main__.MyBytes

    In [5]: a = bytes(b'123')

    In [6]: b = MyBytes(b'123')

    In [7]: a
    Out[7]: b'123'

    In [8]: b
    Out[8]: b'123'

    In [9]: a == b
    Out[9]: True

    In [10]: import sys

    In [11]: sys.getsizeof(a)
    Out[11]: 36

    In [12]: sys.getsizeof(b)
    Out[12]: 52

So with `cdef class` we gain more control and optimize memory usage.

This was not done before because cython forbids to `cdef class X(bytes)` due to
https://github.com/cython/cython/issues/711. We work it around in setup.py with
draft for proper patch pre-posted to upstream in https://github.com/cython/cython/pull/5212 .

Before:

    (z-dev) kirr@deca:~/src/tools/go/pygolang$ gpython -X gpython.zzz
    Traceback (most recent call last):
      File "/home/kirr/src/wendelin/venv/z-dev/bin/gpython", line 3, in <module>
        from gpython import main; main()
      File "/home/kirr/src/tools/go/pygolang/gpython/__init__.py", line 397, in main
        raise RuntimeError('gpython: unknown -X option %s' % opt)
    RuntimeError: gpython: unknown -X option -X                                        <-- NOTE

After:

    (z-dev) kirr@deca:~/src/tools/go/pygolang$ gpython -X gpython.zzz
    Traceback (most recent call last):
      File "/home/kirr/src/wendelin/venv/z-dev/bin/gpython", line 3, in <module>
        from gpython import main; main()
      File "/home/kirr/src/tools/go/pygolang/gpython/__init__.py", line 397, in main
        raise RuntimeError('gpython: unknown -X option %s' % arg)
    RuntimeError: gpython: unknown -X option gpython.zzz                               <-- NOTE

gpython: Fix `gpython -X gpython.runtime=threads` to spawn subinterpreters with threads runtime by default

Previously it was not the case and gpython with default being gevent
runtime was spawned even if parent gpython was instructed to use threads runtime:

    (z-dev) kirr@deca:~/src/tools/go/pygolang$ gpython -X gpython.runtime=threads
    Python 2.7.18 (default, Apr 28 2021, 17:39:59)
    [GCC 10.2.1 20210110] [GPython 0.1] [threads] on linux2
    Type "help", "copyright", "credits" or "license" for more information.
    (InteractiveConsole)
    >>> import sys
    >>> sys.version
    '2.7.18 (default, Apr 28 2021, 17:39:59) \n[GCC 10.2.1 20210110] [GPython 0.1] [threads]'   <-- NOTE threads
    >>> import subprocess
    subprocess.call(sys.executable)ble)
    Python 2.7.18 (default, Apr 28 2021, 17:39:59)
    [GCC 10.2.1 20210110] [GPython 0.1] [gevent 21.1.2] on linux2                               <-- NOTE gevent
    Type "help", "copyright", "credits" or "license" for more information.
    (InteractiveConsole)
    >>>

Factor-out subroutine to run tfunc in subprocess interpreter spawned with
`-X xopt=xval`. This helps clarity and later in addition to `-X
gpython.runtime` we will also need it to verify `-X gpython.strings`.

Previously test_strings_methods was testing a method via comparing bstr
and ustr results of .method() with similar result of unicode.method().
This works reasonably ok. However under gpython, when unicode will be
replaced with ustr, it will no longer compare results of bstr/ustr
methods with something good and external - indeed in that case bstr/ustr
.method() will be compared to result of ustr.method() which opens the
door for bugs to stay unnoticed.

-> Adjust the test to explicitly provide expected result for all entries
in the test vector. We make sure those results are good and match std
python because we also assert that unicode.method() matches it.

On py2 str.decode('string-escape') returns str, not unicode and this
property is actually being used and relied upon by Lib/pickle.py:

https://github.com/python/cpython/blob/v2.7.18-0-g8d21aa21f2c/Lib/pickle.py#L967-L977

We promised bstr to be drop-in replacement for str on py2, so let's
adjust its behaviour to match the original because if we do not,
unpickling strings will break when str is replaced by bstr under
gpython.

Do not add bstr.encode yet until we hit a real case where it is actually used.

repr(ustr|bstr) will change behaviour depending on whether we are
running under regular python, or gpython with string types replaced by
bstr/ustr. But this test is completely orthogonal to that. -> Let's
untie it from particular repr behaviour by emitting verified items in
quoted form + asserting their types in the code.

In ebd18f3f the code was ok but there is a thinko in test: it needs to
test all pickle protocols from 0 to _including_ HIGHEST_PROTOCOL.

    + ./trun python -m pytest -vvsx golang/golang_str_test.py
    ==================================== test session starts =====================================
    platform linux2 -- Python 2.7.18, pytest-4.6.11, py-1.11.0, pluggy-0.13.1 -- /home/kirr/src/tools/go/py2d.venv2023/bin/python
    cachedir: .pytest_cache
    rootdir: /home/kirr/src/tools/go/pygolang-xgpystr
    collected 64 items

    golang/golang_str_test.py::test_strings_basic Traceback (most recent call last):
      File "golang/_golang_str.pyx", line 2270, in golang._golang._xuniord
        return ord(u)
    ValueError: only single character unicode strings can be converted to Py_UCS4, got length 2
    Exception ValueError: 'only single character unicode strings can be converted to Py_UCS4, got length 2' in 'golang._golang._utf8_decode_rune' ignored

    (py2d.venv2023) kirr@deca:~/src/tools/go/pygolang-xgpystr$ python
    Python 2.7.18 (tags/2.7-dirty:8d21aa21f2c, Mar 30 2023, 07:38:40)
    [GCC 10.2.1 20210110] on linux2
    Type "help", "copyright", "credits" or "license" for more information.
    >>> from pygolang import *
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    ImportError: No module named pygolang
    >>> from golang import *
    >>> ord('xy')
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: ord() expected a character, but string of length 2 found
    >>> ord(b'xy')
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: ord() expected a character, but string of length 2 found
    >>> ord(u'xy')
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: ord() expected a character, but string of length 2 found
    >>> ord(b('xy'))
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: ord() expected a character, but string of length 2 found
    >>> ord(u('xy'))
    Traceback (most recent call last):
      File "golang/_golang_str.pyx", line 2270, in golang._golang._xuniord
        return ord(u)
    ValueError: only single character unicode strings can be converted to Py_UCS4, got length 2
    Exception ValueError: 'only single character unicode strings can be converted to Py_UCS4, got length 2' in 'golang._golang._utf8_decode_rune' ignored
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "golang/_golang_str.pyx", line 157, in golang._golang.pyu
        us = _pyu(pyustr, s)
      File "golang/_golang_str.pyx", line 195, in golang._golang._pyu
        s = _utf8_decode_surrogateescape(s)
      File "golang/_golang_str.pyx", line 2198, in golang._golang._utf8_decode_surrogateescape
        emit(_xunichr(r))
      File "golang/_golang_str.pyx", line 2286, in golang._golang._xunichr
        return unichr(0xd800 + (uh >> 10)) + \
    ValueError: unichr() arg not in range(0x10000) (narrow Python build)

It was broken in 50b8cb7e (strconv: Move functionality related to UTF8 encode/decode into _golang_str)

Pygolang stopped to work on Windows in 2019 starting from 8fa3c15b (Start using
Cython and providing Cython/nogil API). Restore it now.

Linux and macOS was working before. And we just added Windows support in
the previous patches.

When underlying pygfobj is FileObjectThread its .readinto() leads to
deadlock because it is no cooperative(*). This manifests as
test_pyx_os_pipe_cpp hang when run by gpython on windows.

-> Workaround this by reading first into intermediate buffer and then
copying data to buffer that user provided.

After this the deadlock is gone but test_pyx_os_pipe_cpp starts to fail
and crash randomly. That's because similarly to channels we need to
care and not access a buffer if it is located on stack and owning
greenlet is inactive. Because when a greenlet is inactive, its stack is
reused by another active greenlet and writing/reading to on-stack memory
accesses that second greenlet stack, corrupting it on write.

-> do the same what we do in chan operations: use intermediate on-heap
buffer to protect original user's buffer to be accesses because it might
be located on stack. That's what actually happens in
test_pyx_os_pipe_cpp where two goroutines read and write to each other
via pipe and using on-stack located buffers. And becuase on windows
pipes, like regular files, are wrapped with FileObjectThread, when
reading greenlet becomes suspended waiting for read reasul, it will be
another greenlet to run on its stack, write to another end of a pipe,
wakeup IO thread, which will write the data to requested buffer on G1
stack and oops - it was G2 there.

(*) see https://github.com/gevent/gevent/pull/1948 for details

Because on Windows it is \ and using / for it to scan in path fails and
leads to test_pymain_opt failure:

     E             Full diff:
     E               [
     E                'sys.flags.debug:      0',
     E                'sys.flags.optimize:   0',
     E                '__debug__:            True',
     E                'assert:               True',
     E                'docstrings:           True',
     E                'import mod.py:        '
     E             -  'C:\\users\\kirr\\Temp\\modpy_imports_fromvmgs8go4\\__pycache__/mod.cpython-310.pyc',
     E             ?                                            ^^  ----
     E             +  'C:\\users\\kirr\\Temp\\modpy_imports_from850gb81s\\__pycache__/mod.cpython-310.pyc',
     E             ?                                            ^^^ +++
     E               ]

Here the difference is because gpython/testprog/print_opt.py failed to
detect tmpd prefix and strip it.

In several places we were preparing repr of a string as '%s' which works
ok most of the time but leads to failure if string contains '\'
characters e.g. if it represents a path and we are running on windows:

        def test_pymain():
            from golang import b

            ....

            # -m <module>
            _ = pyout(['-m', 'hello', 'abc', 'def'], cwd=testdata)
            # realpath rewrites e.g. `local/lib -> lib` if local/lib is symlink
            hellopy = realpath(join(testdata, 'hello.py'))
    >       assert _ == b"hello\nworld\n['%s', 'abc', 'def']\n" % b(hellopy)
    E       assert b"hello\nworld\n['Z:\\\\home\\\\kirr\\\\src\\\\tools\\\\go\\\\pygo-win\\\\pygolang\\\\gpython\\\\testdata\\\\hello.py', 'abc', 'def'
    ]\n" == b"hello\nworld\n['Z:\\home\\kirr\\src\\tools\\go\\pygo-win\\pygolang\\gpython\\testdata\\hello.py', 'abc', 'def']\n"
    E         At index 17 diff: b'\\' != b'h'
    E         Full diff:
    E           (
    E         -  b"hello\nworld\n['Z:\\home\\kirr\\src\\tools\\go\\pygo-win\\pygolang\\gpytho"
    E         ?                                                                  ------------
    E         +  b"hello\nworld\n['Z:\\\\home\\\\kirr\\\\src\\\\tools\\\\go\\\\pygo-win\\\\pygo"
    E         ?                        ++    ++        ++   ++         ++  ++            ++
    E         -  b"n\\testdata\\hello.py', 'abc', 'def']\n",
    E         +  b"lang\\\\gpython\\\\testdata\\\\hello.py', 'abc', 'def']\n",
    E         ?    ++ ++++++++++++++            ++
    E           )

    gpython\gpython_test.py:183: AssertionError

-> Fix it by preparing repr via repr(...) properly.

On Windows if geventmp is present gpython startup fails:

    (1.wenv) Z:\home\kirr\src\tools\go\pygo-win\pygolang>gpython
    Traceback (most recent call last):
      File "C:\Program Files\Python310\lib\runpy.py", line 196, in _run_module_as_main
        return _run_code(code, main_globals, None,
      File "C:\Program Files\Python310\lib\runpy.py", line 86, in _run_code
        exec(code, run_globals)
      File "Z:\home\kirr\src\tools\go\pygo-win\1.wenv\Scripts\gpython.exe\__main__.py", line 7, in <module>
      File "Z:\home\kirr\src\tools\go\pygo-win\pygolang\gpython\__init__.py", line 450, in main
        pymain(argv, init)
      File "Z:\home\kirr\src\tools\go\pygo-win\pygolang\gpython\__init__.py", line 223, in pymain
        init()
      File "Z:\home\kirr\src\tools\go\pygo-win\pygolang\gpython\__init__.py", line 428, in init
        _ = monkey.patch_all(thread=patch_thread)      # XXX sys=True ?
      File "Z:\home\kirr\src\tools\go\pygo-win\1.wenv\lib\site-packages\gevent\monkey.py", line 1255, in patch_all
        _notify_patch(events.GeventWillPatchAllEvent(modules_to_patch, kwargs), _warnings)
      File "Z:\home\kirr\src\tools\go\pygo-win\1.wenv\lib\site-packages\gevent\monkey.py", line 190, in _notify_patch
        notify_and_call_entry_points(event)
      File "Z:\home\kirr\src\tools\go\pygo-win\1.wenv\lib\site-packages\gevent\events.py", line 105, in notify_and_call_entry_points
        subscriber(event)
      File "Z:\home\kirr\src\tools\go\pygo-win\1.wenv\lib\site-packages\geventmp\monkey.py", line 160, in _patch_mp
        _patch_module("_mp.3._mp_util", _patch_module=True, _package_prefix='geventmp.')
      File "Z:\home\kirr\src\tools\go\pygo-win\1.wenv\lib\site-packages\geventmp\monkey.py", line 121, in _patch_module
        gevent_module = import_module(_package_prefix + name)
      File "C:\Program Files\Python310\lib\importlib\__init__.py", line 126, in import_module
        return _bootstrap._gcd_import(name[level:], package, level)
      File "<frozen importlib._bootstrap>", line 1050, in _gcd_import
      File "<frozen importlib._bootstrap>", line 1027, in _find_and_load
      File "<frozen importlib._bootstrap>", line 1006, in _find_and_load_unlocked
      File "<frozen importlib._bootstrap>", line 688, in _load_unlocked
      File "<frozen importlib._bootstrap_external>", line 883, in exec_module
      File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
      File "Z:\home\kirr\src\tools\go\pygo-win\1.wenv\lib\site-packages\geventmp\_mp\3\_mp_util.py", line 16, in <module>
        from gevent.os import _watch_child
    ImportError: cannot import name '_watch_child' from 'gevent.os' (Z:\home\kirr\src\tools\go\pygo-win\1.wenv\lib\site-packages\gevent\os.py)

That happens because geventmp does not support windows actually.

-> Fix it by requiring geventmp to be present only on non-windows.

Adjust related comment as https://github.com/karellen/geventmp/pull/2 has been merged long ago.

On windows setuptools install gpython.exe and gpython-script.py while
pip/distlib install gpython.exe with gpython-script sometimes embedded
into gpython.exe itself with argv[0] pointing to 'gpython' without .exe
suffix. This leads to gpython startup failure:

    (1.wenv) Z:\home\kirr\src\tools\go\pygo-win\pygolang>gpython
    Traceback (most recent call last):
      File "C:\Program Files\Python310\lib\runpy.py", line 196, in _run_module_as_main
        return _run_code(code, main_globals, None,
      File "C:\Program Files\Python310\lib\runpy.py", line 86, in _run_code
        exec(code, run_globals)
      File "Z:\home\kirr\src\tools\go\pygo-win\1.wenv\Scripts\gpython.exe\__main__.py", line 7, in <module>
      File "Z:\home\kirr\src\tools\go\pygo-win\pygolang\gpython\__init__.py", line 437, in main
        pymain(argv, init)
      File "Z:\home\kirr\src\tools\go\pygo-win\pygolang\gpython\__init__.py", line 79, in pymain
        if not _is_buildout_script(exe):
      File "Z:\home\kirr\src\tools\go\pygo-win\pygolang\gpython\__init__.py", line 442, in _is_buildout_script
        with open(path, 'rb') as f:
    FileNotFoundError: [Errno 2] No such file or directory: 'Z:\\home\\kirr\\src\\tools\\go\\pygo-win\\1.wenv\\Scripts\\gpython'

    (1.wenv) Z:\home\kirr\src\tools\go\pygo-win\pygolang>dir ../1.wenv/scripts/gpython*

    Directory of Z:\home\kirr\src\tools\go\pygo-win\1.wenv\scripts

    26.04.2023     14:17       108,404  gpython.exe
           1 file                   108,404 bytes
           0 directories     88,508,866,560 bytes free

-> Adjust pymain to handle this case accordingly.

On windows upon terminating signal reception exict code of the process
is always 3 instead of -signo. And so test_signal_all was failing as

        def test_signal_all():
            retcode, out, _ = _pyrun([dir_testprog + "/signal_test_all.py"], stdout=PIPE)
            assert b"ok (notify)"        in out
            assert b"ok (ignore)"        in out
            assert b"terminating ..."    in out
    >       assert retcode == -syscall.SIGTERM.signo
    E       assert 3 == -15
    E        +  where 15 = os.Signal(15).signo
    E        +    where os.Signal(15) = syscall.SIGTERM

- There is no e.g. signal.SIGKILL on windows:

    golang/os/signal_test.py::test_signal_all Traceback (most recent call last):
      File "Z:\home\kirr\src\tools\go\pygo-win\pygolang\golang\os\testprog\signal_test_all.py", line 82, in <module>
        main()
      File "Z:\home\kirr\src\tools\go\pygo-win\pygolang\golang\os\testprog\signal_test_all.py", line 39, in main
        allsigv.remove(syscall.SIGKILL) # SIGKILL/SIGSTOP cannot be caught
    AttributeError: module 'golang.syscall' has no attribute 'SIGKILL'. Did you mean: 'SIGILL'?

  -> filter-out signals conditionally depending on their presence.

- Need to also filter-out SIGILL/SIGABRT because upon reception MSVC
  runtime terminates process.

Because on Windows os.kill unconditionally terminates target process,
even if own self, instead of sending it any kind of signal.

We use SIGUSR1/SIGUSR2 mainly in this test, but those signals are not
available on Windows:

        @func
        def test_signal():
            # Notify/Stop with wrong chan dtype -> panic
            _ = panics("pychan: channel type mismatch")
    >       with _:  signal.Notify(chan(2), syscall.SIGUSR1)
    E       AttributeError: module 'golang.syscall' has no attribute 'SIGUSR1'

-> Use SIGTERM/SIGINT if SIGUSR1/SIGUSR2 are not available.

Don't want to use SIGTERM/SIGINT unconditionally because those signals are
better to leave for the job control so that e.g. nxdtest can properly kill
spawned pygolang tests.

On Windows in text mode files are opened with encoding=locale.getdefaultlocale()
which is CP125X instead of UTF-8 even if $PYTHONIOENCODING=UTF-8. This
way e.g. test_strings_print fail as:

    E           Failed: not equal:
    E           Expected:
    E               print(qq(b)): "привет αβγ b"
    E               print(qq(u)): "привет αβγ u"
    E           Got:
    E               print(qq(b)): "привет αβγ b"
    E               print(qq(u)): "привет αβγ u"

where "Expected" was read from golang/testprog/golang_test_str.txt and
decoded wrongly.

-> Fix it by always opening files for reading in binary mode and
utf8-decoding manually, if needed, everywhere.

golang: tests: Spawn subprocess python with $PYTHONIOENCODING set to encoding of stdin/stdout/stderr

We need to do it because on Windows `python x.py | ...` runs with stdio
encoding set to cp125X even if just `python x.py` runs with stdio
encoding=UTF-8.

    (1.wenv) Z:\home\kirr\src\tools\go\pygo-win\pygolang\golang\testprog>python golang_test_str.py
    print(qq(b)): "привет b"
    print(qq(u)): "привет u"

    (1.wenv) Z:\home\kirr\src\tools\go\pygo-win\pygolang\golang\testprog>python golang_test_str.py |more
    print(qq(b)): "яЁштхЄ b"
    print(qq(u)): "яЁштхЄ u"

    (1.wenv) Z:\home\kirr\src\tools\go\pygo-win\pygolang\golang\testprog>python golang_test_str.py >aaa.txt
    (1.wenv) Z:\home\kirr\src\tools\go\pygo-win\pygolang\golang\testprog>type aaa.txt
    print(qq(b)): "яЁштхЄ b"
    print(qq(u)): "яЁштхЄ u"

Which leads to the following test_strings_print failure:

    E           Failed: not equal:
    E           Expected:
    E               print(qq(b)): "привет b"
    E               print(qq(u)): "привет u"
    E           Got:
    E               print(qq(b)): "������ b"
    E               print(qq(u)): "������ u"

We also change golang_test_str.py to print not only russian and english
letters, but also greek ones. This is to make sure that stdout IO encoding would
not go cp125X unnoticed because then printing will fail with UnicodeEncodeError.

Note: in the above example both got and expected are wrong. Via
$PYTHONIOENCODING we only fix "got" and we will fix "expected" in the followup
patch. After current patch test_strings_print result is

    E           Failed: not equal:
    E           Expected:
    E               print(qq(b)): "привет αβγ b"
    E               print(qq(u)): "привет αβγ u"
    E           Got:
    E               print(qq(b)): "привет αβγ b"
    E               print(qq(u)): "привет αβγ u"

Apparently on Windows pytest detects terminal width differently than on
Linux/macOS and the test fails as

    E           Failed: not equal:
    E           Differences (unified diff with -expected +actual):
    E               @@ -1,5 +1,12 @@
    E               -...
    E               -_____________________________________ main _____________________________________
    E               -../__init__.py:...: in _
    E               +============================= test session starts =============================
    E               +platform win32 -- Python 3.10.11, pytest-7.3.1, pluggy-1.0.0
    E               +rootdir: PYGOLANG
    E               +collected 1 item
    E               +<BLANKLINE>
    E               +golang_test_defer_excchain.py F                                          [100%]
    E               +<BLANKLINE>
    E               +================================== FAILURES ===================================
    E               +____________________________________ main _____________________________________
    E               +../__init__.py:106: in _
    E                    return f(*argv, **kw)
    E                golang_test_defer_excchain.py:42: in main
    E               @@ -8,6 +15,6 @@
    E                <BLANKLINE>
    E                During handling of the above exception, another exception occurred:
    E               -../__init__.py:...: in __exit__
    E               -    ...
    E               +../__init__.py:183: in __exit__
    E               +    d()
    E                golang_test_defer_excchain.py:31: in d1
    E                    raise RuntimeError("d1: aaa")
    E               @@ -15,9 +22,9 @@
    E                <BLANKLINE>
    E                During handling of the above exception, another exception occurred:
    E               -../__init__.py:...: in __exit__
    E               -    ...
    E               +../__init__.py:183: in __exit__
    E               +    d()
    E                golang_test_defer_excchain.py:33: in d2
    E                    1/0
    E               -E   ZeroDivisionError: ...
    E               +E   ZeroDivisionError: division by zero
    E                <BLANKLINE>
    E                During handling of the above exception, another exception occurred:
    E               @@ -25,3 +32,5 @@
    E                    raise RuntimeError("d3: bbb")
    E                E   RuntimeError: d3: bbb
    E               -=========================== ...
    E               +=========================== short test summary info ===========================
    E               +FAILED golang_test_defer_excchain.py::main - RuntimeError: d3: bbb
    E               +============================== 1 failed in 1.45s ==============================

-> Fix it by not requesting header to be of particular width.

On windows print emits \r\n instead of just \n. Here is how e.g.
test_defer_excchain_dump fails without normalization:

    E           Failed: not equal:
    E           Differences (unified diff with -expected +actual):
    E               @@ -1,42 +1,43 @@
    E               -Traceback (most recent call last):
    E               -  File "PYGOLANG/golang/__init__.py", line ..., in _
    E               -    return f(*argv, **kw)
    E               -  File "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 42, in main
    E               -    raise RuntimeError("err")
    E               -RuntimeError: err
    E               -<BLANKLINE>
    E               -During handling of the above exception, another exception occurred:
    E               -<BLANKLINE>
    E               -Traceback (most recent call last):
    E               -  File "PYGOLANG/golang/__init__.py", line ..., in __exit__
    E               -    ...
    E               -  File "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 31, in d1
    E               -    raise RuntimeError("d1: aaa")
    E               -RuntimeError: d1: aaa
    E               -<BLANKLINE>
    E               -During handling of the above exception, another exception occurred:
    E               -<BLANKLINE>
    E               -Traceback (most recent call last):
    E               -  File "PYGOLANG/golang/__init__.py", line ..., in __exit__
    E               -    ...
    E               -  File "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 33, in d2
    E               -    1/0
    E               -ZeroDivisionError: ...
    E               -<BLANKLINE>
    E               -During handling of the above exception, another exception occurred:
    E               -<BLANKLINE>
    E               -Traceback (most recent call last):
    E               -  ... "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 45, in <module>
    E               -    main()
    E               -  ...
    E               -  File "PYGOLANG/golang/__init__.py", line ..., in _
    E               -    with __goframe__:
    E               -  File "PYGOLANG/golang/__init__.py", line ..., in __exit__
    E               -    ...
    E               -  File "PYGOLANG/golang/__init__.py", line ..., in __exit__
    E               -    ...
    E               -  File "PYGOLANG/golang/__init__.py", line ..., in __exit__
    E               -    ...
    E               -  File "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 35, in d3
    E               -    raise RuntimeError("d3: bbb")
    E               -RuntimeError: d3: bbb
    E               +Traceback (most recent call last):
    E               +  File "PYGOLANG/golang/__init__.py", line 106, in _
    E               +    return f(*argv, **kw)
    E               +  File "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 42, in main
    E               +    raise RuntimeError("err")
    E               +RuntimeError: err
    E               +
    E               +During handling of the above exception, another exception occurred:
    E               +
    E               +Traceback (most recent call last):
    E               +  File "PYGOLANG/golang/__init__.py", line 183, in __exit__
    E               +    d()
    E               +  File "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 31, in d1
    E               +    raise RuntimeError("d1: aaa")
    E               +RuntimeError: d1: aaa
    E               +
    E               +During handling of the above exception, another exception occurred:
    E               +
    E               +Traceback (most recent call last):
    E               +  File "PYGOLANG/golang/__init__.py", line 183, in __exit__
    E               +    d()
    E               +  File "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 33, in d2
    E               +    1/0
    E               +ZeroDivisionError: division by zero
    E               +
    E               +During handling of the above exception, another exception occurred:
    E               +
    E               +Traceback (most recent call last):
    E               +  File "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 45, in <module>
    E               +    main()
    E               +  File "Z:\home\kirr\src\tools\go\pygo-win\1.wenv\lib\site-packages/decorator.py", line 232, in fun
    E               +    return caller(func, *(extras + args), **kw)
    E               +  File "PYGOLANG/golang/__init__.py", line 105, in _
    E               +    with __goframe__:
    E               +  File "PYGOLANG/golang/__init__.py", line 182, in __exit__
    E               +    with __goframe__:
    E               +  File "PYGOLANG/golang/__init__.py", line 182, in __exit__
    E               +    with __goframe__:
    E               +  File "PYGOLANG/golang/__init__.py", line 183, in __exit__
    E               +    d()
    E               +  File "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 35, in d3
    E               +    raise RuntimeError("d3: bbb")
    E               +RuntimeError: d3: bbb

Else on Windows e.g. test_defer_excchain_traceback fails as

    E           Failed: not equal:
    E           Differences (unified diff with -expected +actual):
    E               @@ -1,8 +1,8 @@
    E                Traceback (most recent call last):
    E               -  File "PYGOLANG/golang/golang_test.py", line ..., in test_defer_excchain_traceback
    E               +  File "PYGOLANG\golang\golang_test.py", line 1524, in test_defer_excchain_traceback
    E                    alpha()
    E               -  File "PYGOLANG/golang/golang_test.py", line ..., in alpha
    E               +  File "PYGOLANG\golang\golang_test.py", line 1521, in alpha
    E                    beta()
    E               -  File "PYGOLANG/golang/golang_test.py", line ..., in beta
    E               +  File "PYGOLANG\golang\golang_test.py", line 1520, in beta
    E                    raise RuntimeError("gamma")
    E                RuntimeError: gamma

Else it fails to import on Windows:

    collecting ... 05c8:err:module:import_dll Library libgolang.dll (which is needed by L"Z:\\home\\kirr\\src\\tools\\go\\pygo-win\\pygolang\\golang\\_golang.cp310-win_amd64.pyd") not found
    collected 0 items / 1 error

    =========================================================== ERRORS ===========================================================
    ___________________________________________ ERROR collecting golang/golang_test.py ___________________________________
    ImportError while importing test module 'Z:\home\kirr\src\tools\go\pygo-win\pygolang\golang\golang_test.py'.
    Hint: make sure your test modules/packages have valid Python names.
    Traceback:
    C:\Program Files\Python310\lib\importlib\__init__.py:126: in import_module
        return _bootstrap._gcd_import(name[level:], package, level)
    golang\__init__.py:45: in <module>
        from golang._golang import _pysys_exc_clear as _sys_exc_clear
    E   ImportError: DLL load failed while importing _golang: Модуль не найден.

We need to increase required setuptools_dso version because dylink_prepare_dso
and generation of *_dsoinfo.py modules was done after setuptools_dso 2.

On Windows this files are generated when linking alongside *.dll files
if there are exported symbols.

See also https://github.com/mdavidsaver/setuptools_dso/pull/25.

Libpyxruntime by definition contains python-specific code and we already
compile it with include path having python includes in it. However on
windows pyconfig.h contains

    #pragma comment(lib,"python3.lib")

which instructs the linker to automatically link to that library. And
without proper library path the link fails:

    Z:\home\kirr\src\tools\go\pygo-win\BuildTools\vc\tools\msvc\14.35.32215\bin\Hostx64\x64\link.exe /nologo /INCREMENTAL:NO /LTCG /DLL /MANIFEST:EMBED,ID=2 /MANIFESTUAC:NO /LIBPATH:build\lib.win-amd64-cpython-31
    0\golang\runtime /LIBPATH:z:\home\kirr\src\tools\go\pygo-win\BuildTools\vc\tools\msvc\14.35.32215\lib\x64 /LIBPATH:z:\home\kirr\src\tools\go\pygo-win\BuildTools\kits\10\lib\10.0.22000.0\ucrt\x64 /LIBPATH:z:\h
    ome\kirr\src\tools\go\pygo-win\BuildTools\kits\10\lib\10.0.22000.0\um\x64 libgolang.lib build\temp.win-amd64-cpython-310\Release\golang/runtime/libpyxruntime.obj /OUT:build\lib.win-amd64-cpython-310\golang\ru
    ntime\libpyxruntime.dll /IMPLIB:build\lib.win-amd64-cpython-310\golang\runtime\libpyxruntime.lib
    LINK : fatal error LNK1104: cannot open file 'python310.lib'

-> Fix it by providing proper library path for python.dll .

We need to do it ourselves only for libpyxruntime dso because for py
extensions this is automatically done by distutils out of the box.

On Windows rthere is no fcntl

    golang/runtime\_runtime_gevent.cpp(4811): error C3861: 'S_ISBLK': identifier not found
    golang/runtime\_runtime_gevent.cpp(4823): error C2039: 'Fcntl': is not a member of 'golang::internal::syscall'
    .\golang/runtime/internal/syscall.h(36): note: see declaration of 'golang::internal::syscall'
    golang/runtime\_runtime_gevent.cpp(4823): error C2065: 'F_GETFL': undeclared identifier
    golang/runtime\_runtime_gevent.cpp(4823): error C3861: 'Fcntl': identifier not found
    golang/runtime\_runtime_gevent.cpp(4870): error C2065: 'O_ACCMODE': undeclared identifier
    golang/runtime\_runtime_gevent.cpp(4889): error C2039: 'Fcntl': is not a member of 'golang::internal::syscall'
    .\golang/runtime/internal/syscall.h(36): note: see declaration of 'golang::internal::syscall'
    golang/runtime\_runtime_gevent.cpp(4889): error C2065: 'F_SETFL': undeclared identifier
    golang/runtime\_runtime_gevent.cpp(4889): error C2065: 'O_NONBLOCK': undeclared identifier
    golang/runtime\_runtime_gevent.cpp(4889): error C3861: 'Fcntl': identifier not found

and even if there would be gevent does not provide cooperative version
of FileObject for non-POSIX platforms.

-> Always use FileObjectThread on windows even for pipes.