explicitly set UnsupportedOperation's module rather than relying on incorrect globals on startup (closes #14745)

Issue #14716: Change integer overflow check in unicode_writer_prepare()
to compute the limit at compile time instead of runtime. Patch writen by Serhiy
Storchaka.

Issue #14742:  Don't include DirectoryTestCase from test_unparse in test_tools until we can speed it up.

Issue #14583: Fix importlib bug when a package's __init__.py would first import one of its modules then raise an error.

to compute the limit at compile time instead of runtime. Patch writen by Serhiy
Storchaka.

PyAccu API. For example, it makes str.format() from 25% to 30% faster on Linux.

Issue #14700: Fix two broken and undefined-behaviour-inducing overflow checks in old-style string formatting.  Thanks Serhiy Storchaka for report and original patch.

Also, add tests for gzip.open().