Fix needs_extensions version comparison to use packaging.Version

[piyushhhxyz]

Summary

Fix the needs_extensions check to compare versions using packaging.version.Version instead of string comparison.

Problem

The needs_extensions check compared version strings lexicographically, which produced incorrect results for versions with components >= 10. For example:

• As strings: '0.6.0' > '0.10.0' evaluates to True (wrong)
• As versions: Version('0.6.0') > Version('0.10.0') evaluates to False (correct)

This caused extensions like sphinx-gallery 0.10.0 to be rejected when 0.6.0 was the minimum required version.

Fix

Replace the string comparison reqversion > extension.version with Version(reqversion) > Version(extension.version) using packaging.version.Version, which is already a dependency of Sphinx.

Files Changed

• sphinx/extension.py -- Use packaging.version.Version for proper semantic version comparison
• tests/test_extension.py -- New test file with regression tests for the version comparison fix

Testing

Unit tests (new)

$ python3 -m pytest tests/test_extension.py -v
tests/test_extension.py::test_verify_needs_extensions_version_comparison PASSED
tests/test_extension.py::test_verify_needs_extensions_unknown_version PASSED
tests/test_extension.py::test_verify_needs_extensions_missing_extension PASSED
3 passed

Manual verification

>>> from packaging.version import Version
>>> Version('0.6.0') > Version('0.10.0')
False  # Correct! 0.6.0 < 0.10.0
>>> '0.6.0' > '0.10.0'
True   # Bug! String comparison is wrong

Existing tests

Ran tests/test_config.py -- all pre-existing failures are unrelated (sphinxcontrib.applehelp version mismatch with this old Sphinx version). Verified by running the same tests on the base commit without changes.