swev-id: sphinx-doc__sphinx-9711 fix needs_extensions version check

[casey-brooks]

Summary

• switch verify_needs_extensions to PEP 440 comparisons using packaging.version.Version with a conservative string fallback for unparseable versions (needs_extensions: use proper semantic version comparison (PEP 440) to fix string-based checks #91)
• add regression coverage for newer, prerelease, unknown, dev, post-release, and equality scenarios via dummy extensions under tests/roots/test_needs_extensions
• confirmed the original gallery build now succeeds with sphinx-gallery==0.10.0

Testing

• pytest tests/test_extension_needs.py -q
• flake8 sphinx/extension.py tests/test_extension_needs.py
• PYTHONPATH=/workspace/sphinx/stubs:/workspace/sphinx sphinx-build -b html -T -v . _build/html

Reproduction

1. Create a minimal project with conf.py:

   extensions = ['sphinx_gallery.gen_gallery']
   needs_extensions = {'sphinx_gallery.gen_gallery': '0.6.0'}
   master_doc = 'index'
   project = 'Needs Extension Repro'

   and an index.rst stub.
2. python3 -m venv .venv && . .venv/bin/activate
3. pip install -e . sphinx-gallery==0.10.0
4. Add a sitecustomize.py (and put its directory on PYTHONPATH) containing:

   import sphinx
   sphinx.__display_version__ = '5.0.0'

   This satisfies the pip-installed sphinxcontrib.* packages that guard on require_sphinx('5.0') while the branch still reports 4.3.0.
5. Place a placeholder examples/README.txt so sphinx-gallery gets past its README check.
6. Run PYTHONPATH=/path/to/sitecustomize:/workspace/sphinx sphinx-build -b html -T -v . _build/html.

Observed failure (before fix)

Running Sphinx v5.0.0

Traceback (most recent call last):
  File "/workspace/sphinx/sphinx/cmd/build.py", line 276, in build_main
    app = Sphinx(args.sourcedir, args.confdir, args.outputdir,
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/workspace/sphinx/sphinx/application.py", line 261, in __init__
    self.events.emit('config-inited', self.config)
  File "/workspace/sphinx/sphinx/events.py", line 101, in emit
    results.append(listener.handler(self.app, *args))
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/workspace/sphinx/sphinx/extension.py", line 55, in verify_needs_extensions
    raise VersionRequirementError(__('This project needs the extension %s at least in '
sphinx.errors.VersionRequirementError: This project needs the extension sphinx_gallery.gen_gallery at least in version 0.6.0 and therefore cannot be built with the loaded version (0.10.0).

Sphinx version error:
This project needs the extension sphinx_gallery.gen_gallery at least in version 0.6.0 and therefore cannot be built with the loaded version (0.10.0).

After fix

• PYTHONPATH=/path/to/sitecustomize:/workspace/sphinx sphinx-build -b html -T -v . _build/html
  → build succeeded.

[casey-brooks]

Test & Lint

• pytest tests/test_extension_needs.py -q (5 passed)
• flake8 sphinx/extension.py tests/test_extension_needs.py (no issues)

[noa-lucent]

Looks good to me. Thanks for adding robust version comparisons and thorough tests covering the new behavior.