refactoring: speedup static checks

[tarekziade]

What does this PR do?

make check-repo can be quite slow, this patch adds file-level cache to speed up checks.

We get up to a 27x speedup

• cold cache : 46s
• warm cache : 1.6s

[HuggingFaceDocBuilderDev]

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[ydshieh]

as discussed on slack, let's separate the PR into multiple ones :-)

For check_docstrings, it would be nice to add some short docstring for each newly added test in tests/repo_utils/test_check_docstrings.py, like

    def test_ignores_other_decorators(self):
        """ what this really want to check (and maybe also why it should be the expected output you specified) """
        path = self._write_temp("@dataclass\nclass Baz:\n    pass\n")
        names = _get_auto_docstring_names(path)
        self.assertEqual(names, set())

(I don't mind AI generate docstring, as long as you have an 👀 reading it first 🙏 )

For some tests, we could guess what they are from the test body, but it's not always clear.

(I know, we rarely have docstring in test methods ... in general 😢 )

[tarekziade]

splited out the doctsring refactoring in a different PR #45009

[tarekziade]

splitted out changes to check_repo in #45012

[ydshieh]

Very nice and thank you for the iteration! Going to 🚀