[models] Change default model to fast_base - soft breaking change

[felixdittrich92]

This PR:

• changes the default detection model from db_resnet50 to fast_base
• reason:
  • more accure (actually much much better also on rotated samples) / needs less memory / small bit faster

Any feedback is welcome 🤗

NOTE: marked as breaking change because with the next release we should mention this change and to revert to the previous behavior that it only requires to pass db_resnet50 as det_arch

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.35%. Comparing base (bf82d63) to head (ef294f1).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1588      +/-   ##
==========================================
+ Coverage   96.33%   96.35%   +0.01%     
==========================================
  Files         163      163              
  Lines        7702     7702              
==========================================
+ Hits         7420     7421       +1     
+ Misses        282      281       -1     

Flag	Coverage Δ
unittests	96.35% <ø> (+0.01%)	⬆️

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[odulcy-mindee]

Thanks !