feat: Add localpart to CSV import

[jannden]

Closes #96

Changes:

1. Added localpart field to the User struct as an optional field
2. Modified CSV import to store the localpart from CSV as metadata as localpart
3. Updated creation of new users in Zitadel to use localpart as Zitadel user ID
4. Emitting warning when attempting to update a user with a different localpart
5. Updated unit and e2e tests to verify

[codecov]

Codecov Report

Attention: Patch coverage is 92.91339% with 9 lines in your changes missing coverage. Please review.

Project coverage is 93.18%. Comparing base (f6ffe7c) to head (b267043).
Report is 2 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/sources/csv.rs	86.76%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #100      +/-   ##
==========================================
- Coverage   93.26%   93.18%   -0.09%     
==========================================
  Files           9        9              
  Lines        1604     1716     +112     
==========================================
+ Hits         1496     1599     +103     
- Misses        108      117       +9     

Files with missing lines	Coverage Δ
src/bin/migrate.rs	98.83% <100.00%> (+0.11%)	⬆️
src/lib.rs	87.12% <100.00%> (+0.72%)	⬆️
src/sources/ldap.rs	97.86% <100.00%> (+<0.01%)	⬆️
src/user.rs	92.56% <100.00%> (+0.90%)	⬆️
src/zitadel.rs	96.73% <100.00%> (+0.09%)	⬆️
src/sources/csv.rs	94.79% <86.76%> (-4.47%)	⬇️

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[emgrav]

Looks good, many thanks for getting this done so fast! Should we also tag a release in the same PR?