[WIP] Check docstring runs on modular files

[zucchini-nlp]

What does this PR do?

Check docstring currently doesn't check modular files. So if a class is defined in modular without any "copying" and has a bad docstring, we do not check it. Instead we check the auto-generated code, which sometimes is annoying

This is a draft made by a code agent and edited by me. It relies on AST to parse the docstring. I think we can entirely switch to AST so I will try to clean up the check_docstring file. Opening a draft for now to make sure we're not doing duplicate work

fyi @ydshieh

[github-actions]

[For maintainers] Suggested jobs to run (before merge)

run-slow: afmoe, aria, d_fine, glm4v

[HuggingFaceDocBuilderDev]

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