[MISC] Add license file and switch to uv build

[dragomirp]

• Add license file in pyproject to pass uv parts module validatation
• Switch to uv build system

Checklist

• I have added or updated any relevant documentation.
• I have cleaned any remaining cloud resources from my accounts.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 49.65%. Comparing base (40b69ca) to head (958fb61).
⚠️ Report is 1 commits behind head on 16/edge.

❌ Your project status has failed because the head coverage (49.65%) is below the target coverage (70.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@           Coverage Diff            @@
##           16/edge      #40   +/-   ##
========================================
  Coverage    49.65%   49.65%           
========================================
  Files            4        4           
  Lines          860      860           
  Branches        99       99           
========================================
  Hits           427      427           
  Misses         415      415           
  Partials        18       18           

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[dragomirp]

UV plugin complains due to the license not being a file: https://github.com/canonical/pgbouncer-operator/actions/runs/19366235067/job/55410021051?pr=590#step:11:404

[dragomirp]

Defaults to src.

[taurus-forever]

Nice!