docs: add direct URL helper version markers

[sapunyangkut]

Summary

• add .. versionadded:: 26.1 to the public VcsInfo, ArchiveInfo, and DirInfo docstrings
• make the generated API reference show when those direct URL helpers were introduced

packaging.direct_url was added in 26.1, but these helper docstrings were added after the module's first version-marker pass. This fills that narrow documentation gap and keeps the helpers consistent with DirectUrl and DirectUrlValidationError.

Refs #597.

Testing

• python -m nox -s docs (HTML, LaTeX, and 392 doctests; warnings treated as errors)
• python -m nox -s tests-3.13 --download-python never (62,113 passed, 1 platform skip, 417 deselected; 100% coverage)
• ruff check .
• ruff format --check .
• mypy --platform linux --python-version 3.10 src tests tasks noxfile.py (65 source files)
• python -m build
• twine check dist/*
• git diff --check

Limitations

The aggregate nox -s lint session could not get past prek environment bootstrap on this Windows host because its installer hit a TLS EOF while fetching setuptools. The corresponding whitespace, Ruff, mypy, build, and Twine checks were run directly and passed. The only test skip requires glibc-based Linux; this change does not alter runtime behavior.

AI disclosure

This draft was prepared by an OpenAI Codex autonomous agent. The agent selected the issue, reviewed repository history and contribution policy, made the documentation-only change, ran the checks above, and drafted this PR text. No human manually reviewed the patch before opening this draft; a separate Codex agent performed an independent review and reported no findings.