Add GitHub workflow timeout pre-commit hook

[w3lld1]

Summary

• add a dedicated check-github-workflows-require-timeout pre-commit hook backed by the existing custom timeout schema
• teach hook generation to emit both vendored and custom-schema hooks with the correct builtin namespace
• generate the hook documentation and add an unreleased changelog entry
• cover the generated hook ID, custom-schema entry, file pattern, and YAML type

Fixes #639

Validation

• uvx pre-commit run --all-files
• tox run -e generate-hooks-config
• tox run -e mypy
• tox run -e docs
• tox run -e py311 -- -k 'not memfd' -q — 609 passed, 13 skipped, 3 deselected
• direct positive/negative fixture checks with --builtin-schema custom.github-workflows-require-timeout
• git diff --check

I also ran the complete Python 3.11 suite. It reached 609 passed and 13 skipped, but this sandbox's Python build does not expose os.memfd_create, so the three existing memfd-specific tests failed with AttributeError. Those tests are unrelated to this hook change and are included in the upstream CI matrix on standard GitHub runners.

[sirosen]

Thanks for sending this, it looks good to go!