Various CI/deps updates

[danielhollas]

• run dependabot update semianually
• move dev dependencies to 'dev' dependency-group, which uv installs by default
• use uv.lock in CI
• update pre-commit hooks
• Drop Python 3.7

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 49.10%. Comparing base (ba4b78c) to head (8452bd5).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #29      +/-   ##
==========================================
- Coverage   49.12%   49.10%   -0.02%     
==========================================
  Files           3        3              
  Lines         114      112       -2     
==========================================
- Hits           56       55       -1     
+ Misses         58       57       -1     

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