Signed-off-by: Andrew V. Jones <andrew.jones@vector.com>

Closes https://github.com/cython/cython/pull/4101
See https://github.com/cython/cython/issues/4100

* Handle constant folding for LanguageLevel 2 on Python 3. Ensure that when StrNode is a BytesLiteral, that we don't coerce it to unicode.
* Add test for string multiplication bug. Needed to change the TreePath slightly to allow bytes-to-str comparison.

Fixes https://github.com/cython/cython/issues/3951

Remove incorrect dict unpacking optimisation that leaked external dict changes into the result (GH-4091)

Closes https://github.com/cython/cython/issues/3227

* Disable GC-sensitive NumPy tests on PyPy
* Removed @testcase decorator pattern that was causing tests to be run twice

Creating global CDEFS for holding compiler definitions. Then pass it to the distutils.

Also add .vscode folder to .gitignore

Fixes https://github.com/cython/cython/issues/4096

Remove incorrect dict unpacking optimisation that leaked external dict changes into the result (GH-4091)

Closes https://github.com/cython/cython/issues/3227

Closes https://github.com/cython/cython/issues/4113

Replace usage of the seemingly CPython-internal Py_ISSPACE() macro by a dedicated inline function to make it work in C++ (where Py_ISSPACE() fails to link).

Closes https://github.com/cython/cython/issues/4111
Closes https://github.com/cython/cython/pull/4112

* Handle constant folding for LanguageLevel 2 on Python 3. Ensure that when StrNode is a BytesLiteral, that we don't coerce it to unicode.
* Add test for string multiplication bug. Needed to change the TreePath slightly to allow bytes-to-str comparison.

Fixes https://github.com/cython/cython/issues/3951

Fix optimised_pow2_inplace() doctest on Python 3.10 because the error message changed.

Python 3.9 error message:
    unsupported operand type(s) for ** or pow(): 'int' and 'str'

Python 3.10 error message:
    unsupported operand type(s) for **=: 'int' and 'str'

Re-disable third-party integration testing in Py2.6 entirely since most packages aren't compatible anymore (and I don't want to dig up the versions that are).

Freeze the test dependency packages for Python 2.x to prevent further deprecations. More and more packages drop Py2 support these days.

Only #define PY_SSIZE_T_CLEAN if it is not already #defined

Signed-off-by: Andrew V. Jones <andrew.jones@vector.com>

* Reject invalid underscore placements in float parser.
* Add a proper nan/inf float parser to prevent underscore-mixes like "in_f" from passing through.