gh-100150: document that --without-doc-strings affects inspect.signature

[Gh-Novel]

\n* Issue: gh-100150\n\n## Summary\n\nAdds a note to the `--without-doc-strings` configure option documentation explaining that disabling docstrings also prevents `inspect.signature()` from retrieving signatures for built-in functions and methods implemented in C.\n\nThis happens because signatures for C builtins are embedded in their docstrings via the Argument Clinic tool (`__text_signature__` attribute). When docstrings are stripped, the signature metadata is lost.\n\n### Changes\n\n- Added a `.. note::` box to `Doc/using/configure.rst` under `--without-doc-strings`\n- Mentions `inspect.signature()`, `help()`, and third-party framework impact\n- Links to the Argument Clinic documentation in the devguide\n\n### Testing\n\n- Sphinx doc build passes with zero warnings\n- Verified `len.__text_signature__` attribute exists in normal builds and would be `None` without doc strings

---

📚 Documentation preview 📚: https://cpython-previews--144746.org.readthedocs.build/