Fix sphinx-doc__sphinx-9711: needs_extensions checks versions using strings

[piyushhhxyz]

Summary

Fix needs_extensions version comparison to use proper semantic versioning instead of string comparison.

Problem

The verify_needs_extensions function in sphinx/extension.py compared version strings using plain Python string comparison (reqversion > extension.version). This causes incorrect results for multi-digit version components because string comparison is lexicographic:

• '0.6' > '0.10' evaluates to True (because '6' > '1')
• But semantically, version 0.10 is newer than 0.6

This meant extensions at version 0.10+ would be incorrectly rejected when the minimum required version was lower (e.g., 0.6).

Fix

Replace the string comparison with packaging.version.parse() for proper semantic version comparison:

# Before (string comparison - broken)
if extension.version == 'unknown version' or reqversion > extension.version:

# After (semantic version comparison - correct)  
if extension.version == 'unknown version' or parse_version(reqversion) > parse_version(extension.version):

packaging is already a dependency of Sphinx and is used elsewhere in the codebase (e.g., sphinx/ext/doctest.py).

Fixes #9711