gh-116731: libregrtest: Clear inspect & importlib.metadata caches in clear_caches

[encukou]

Thanks to @jaraco for investigation (i.e. the hard part of the fix)

Clearing the inspect caches isn't entirely correct -- see #116804.
This PR is a minimal change to get the buildbots green.

• Issue: With #116680, test_importlib started leaking on refleaks #116731

[jaraco]

This whole long function makes me wonder if Python shouldn't prescribe a protocol for any module to provide cache cleanup, e.g. a __cache_clean method. Then there could be a single routine like at the top:

    for mod in sys.modules.values():
        if hasattr(mod, '__warningregistry__'):
            del mod.__warningregistry__
        with suppress(AttributeError):
            mod.__cache_clean()

Regardless, such a refactor would be out of the scope of this issue.

[jaraco]

Why not importlib_metadata.MetadataPathFinder().invalidate_caches()? I feel like the latter is likely to be more robust if new caches are created.

[encukou]

IMO, that'd make it too easy to add unbounded caches, like those in #116804. The refleak tests should catch those :)

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @encukou for commit 7f58006 🤖

If you want to schedule another build, you need to add the 🔨 test-with-refleak-buildbots label again.

[miss-islington-app]

Thanks @encukou for the PR 🌮🎉.. I'm working now to backport this PR to: 3.12.
🐍🍒⛏🤖

[bedevere-app]

GH-116820 is a backport of this pull request to the 3.12 branch.