✨ [#663] Add command to delete Klantcontacten not related to…

[OlhaZahoruiko]

… Zaken

Fixes #663

Changes

Added a management command to clean up Klantcontacten that are not related to a Zaak, including related records and orphaned Partijen, with dry-run and date filtering options. Added tests for the cleanup behavior.

Checklist

• Commit hygiene

  • Commit messages refer to the relevant Github issue
  • Commit messages explain the "why" of change, not the how

• Architectural design record

  • If a design decision was made that changes functionality, create an architectural design record for it here

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.03%. Comparing base (f2fb412) to head (0af48da).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #664      +/-   ##
==========================================
+ Coverage   98.00%   98.03%   +0.03%     
==========================================
  Files         241      243       +2     
  Lines       14245    14486     +241     
==========================================
+ Hits        13961    14202     +241     
  Misses        284      284              

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