chore: switch to uv and nox

[2bndy5]

• Removes just as the default task runner in favor of nox.
• Uses uv to manage dependencies, which is also used by nox.
• Updated CI and docs/README accordingly.
• Removed all requirements.txt files in favor of using uv to lock dependencies.
• Modified dependabot config to use the new uv.lock file.
• Modified RTD config to use uv and nox.
• Added a CONTRIBUTING.md doc to explain on-boarding

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.47%. Comparing base (851a435) to head (46cff6b).
⚠️ Report is 19 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #145      +/-   ##
==========================================
- Coverage   97.53%   97.47%   -0.06%     
==========================================
  Files          14       14              
  Lines        3406     3406              
==========================================
- Hits         3322     3320       -2     
- Misses         84       86       +2     

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[codspeed-hq]

CodSpeed Performance Report

Merging #145 will not alter performance

_{Comparing migrate-to-uv (46cff6b) with main (49a7c8d)}

Summary

✅ 1 untouched benchmarks

[2bndy5]

Also resolves security report #12 from dependabot (closes #149)