fix: discover non Cargo packages in a Cargo workspace

[esteve]

This PR adds discovery of non-Cargo packages in a Cargo workspace.

Fixes #63

[esteve]

I ran both the Black and Ruff formatters and both replace single quotes with double ones, I'll revert those changes but I wonder if it'd better to update flake8 to match Black and Ruff since both have become the standard for Python formatting.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.70%. Comparing base (ec2b28b) to head (8b12840).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #64      +/-   ##
==========================================
+ Coverage   72.22%   72.70%   +0.47%     
==========================================
  Files           9        9              
  Lines         342      348       +6     
  Branches       59       60       +1     
==========================================
+ Hits          247      253       +6     
  Misses         61       61              
  Partials       34       34              

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