feat: remove datacenter property from server and primary_ip

[lukasmetzner]

Remove the datacenter property from Server and Primary IP resource where possible. The property was deprecated ~6 months ago, and because the property is removed from the API, removing it from our code is not considered a breaking change.

Assisted-by: Claude Opus 4.8

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.37%. Comparing base (41b4e80) to head (04f2fd8).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #890      +/-   ##
==========================================
- Coverage   78.41%   78.37%   -0.04%     
==========================================
  Files          59       59              
  Lines        4368     4361       -7     
==========================================
- Hits         3425     3418       -7     
  Misses        640      640              
  Partials      303      303              

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