Add pre-commit hooks and consolidate dev dependencies

[raphaelvallat]

Add pre-commit hooks and consolidate dev dependencies

Changes

• Add .pre-commit-config.yaml — runs ruff (with --fix) and ruff-format automatically on every commit via ruff-pre-commit
• Consolidate dependency groups — merge test into dev in pyproject.toml; add mpmath and pre-commit to dev
• Update CI workflows and docs — replace --group=test with --group=dev across all GitHub Actions workflows, README.rst, and docs/contributing.rst
• Document pre-commit setup in docs/contributing.rst with install instructions

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.36%. Comparing base (c2a80ba) to head (fa76221).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #506   +/-   ##
=======================================
  Coverage   98.36%   98.36%           
=======================================
  Files          19       19           
  Lines        3304     3304           
  Branches      490      490           
=======================================
  Hits         3250     3250           
  Misses         32       32           
  Partials       22       22           

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