Fix incorrect pyc cache loaded when test file is updated in short time

[jnhyperion]

See: #13292

The root cause is the cache is using file st_mtime int value to check if it's out of date, it's not so accurate when the file is updated in short time. Using st_mtime_ns is the better solution.

[bluetech]

Thanks @jnhyperion, this looks like a good change to me.

Can you please add a changelog entry? (see changelog/README.rst file)

The tests failures are due to #13291, rebasing on main after that PR is merged should make CI pass.

[bluetech]

Sorry I missed it before, but this comment seems to negate this change -- it takes the lower 32 bits while st_mtime_ns needs at least 64 bits, e.g.

>>> import os >>> st = os.stat('/home') >>> print(st.st_mtime_ns) 1669828167393028173 >>> print(st.st_mtime_ns & 0xFFFFFFFF) 23537741 >>> print(int(st.st_mtime) & 0xFFFFFFFF) 1669828167

Basically, the pyc timestamp format is 32 bits, and we are trying to stay compatible with it (even though it's not absolutely necessary as we do our own loading). The same problem occurs with python itself, not just pytest.

See:
python/cpython#121376
https://discuss.python.org/t/change-pyc-file-format-to-record-more-accurate-timestamp-and-other-information/57815

Also related: #11418

[jnhyperion]

You're correct, this is more complex than I expected, I used to run the same test without pytest, but it didn't reproduce somehow, so I thought it's only caused by pytest. Actually, the similar issue still exists in python's import system, and pytest's cache rewrite inherited the same issue. Looks like no proper solution for the issue until now, perhaps we should close the PR.

[nicoddemus]

Closing then as #13293 (comment), we can easily reopen if needed.

Thanks @jnhyperion!