Exclude pyc dirs, not include, when hashing code

[huonw]

This fixes #2285 by fixing a minor typo in f9a9d94 / #2263 that caused the computation of a PEXes code hash to not recur into the correct directories.

I think this explains the symptoms in #2285 due to caching: if a PEX only contains files in subdirectories, the code hash will be da39a3ee5e6b4b0d3255bfef95601890afd80709 (the sha256 hash of no data) and thus potentially the venv create might be referring to an incorrectly cached installation.

[huonw]

I haven't yet got my dev environment to work for running test with the Python 3.12 changes and don't have time to today, so the test is not yet confirmed to be precise (i.e. I don't know if the test fails before/passes after). The bisection script from #2285 does now give expected behaviour, and doesn't without, though.

[jsirois]

My time today is limited as well, but this is certainly a fix of something.

[huonw]

I've got a dev environment working again 🎉

That test was wrong (testing dir_hash, bug was in pex_code_hash). I've rewritten the existing tests for dir_hash to also test pex_code_hash, which catches the bug, plus added an assertion for the hidden file handling.

[jsirois]

... haven't yet got my dev environment to work for running test with the Python 3.12 changes ...

@huonw fwiw, if you have docker, then you need no dev env and can do things just like CI:
https://github.com/pantsbuild/pex/blob/db5b5100d0d739964bfc46943bc9c8f9e1bed480/.github/workflows/ci.yml#L99-L101

Basically:

1. (one time only) BASE_MODE=pull CACHE_MODE=pull ./dtox.sh --version
2. ./dtox.sh ...regular tox args...

You don't need to do step 1, in which case these images will be built locally, but that is slow. If you have a decent network connection, pulling them is probably more convenient. What this nets you is the full suite of Python interpreters Pex supports - both CPython and PyPy - ready to go in the image. It also gets you a pre-seeded PyPI cache when you use ./dtox.sh -epy... -- --devpi .... You can omit the CACHE_MODE=pull if you don't use the --devpi feature of the build or if you'd rather have it build that cache up locally.