Fix Ruff lint violations

[timkpaine]

Description

Fix violations exposed by recent Ruff changes without modifying lint rules. Remove Python 3.10 compatibility code now that Python 3.11 is minimum, make subprocess behavior explicit, and apply Ruff-required simplifications and annotations.

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactor / code cleanup
• CI / build configuration
• Other (describe below)

Checklist

• Linting passes (make lint)
• Tests pass (make test)
• New tests added for new functionality (not applicable; no new functionality)
• Documentation updated (not applicable; no user-facing change)
• Changelog / version bump (not applicable; no release requested)

[github-actions]

Test Results

133 tests  ±0   133 ✅ ±0   7s ⏱️ -1s
  1 suites ±0     0 💤 ±0 
  1 files   ±0     0 ❌ ±0 

Results for commit 2be96b4. ± Comparison against base commit b8ab1a9.

[codecov]

Codecov Report

❌ Patch coverage is 88.23529% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.68%. Comparing base (b8ab1a9) to head (2be96b4).

Files with missing lines	Patch %	Lines
check_dist/_core.py	80.00%	1 Missing ⚠️
check_dist/tests/test_all.py	90.90%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #28      +/-   ##
==========================================
+ Coverage   89.98%   90.68%   +0.70%     
==========================================
  Files           4        4              
  Lines        1048     1041       -7     
  Branches      110      106       -4     
==========================================
+ Hits          943      944       +1     
+ Misses         79       74       -5     
+ Partials       26       23       -3     

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