Major changes to loss functions

[klieret]

This introduces breaking changes to the interface and changes the behavior of the losses.

• Combine all loss calculation into single classes (no more separate classes for BackgroundLoss), including weighting of the different components
• Use faster/more memory-efficient implementations of all losses
• Changing behavior of losses: Two non-important particles can no longer repel each other

Todo:

• [x] Exclude low pt repulsion also in GC embedding
• [x] Bump test coverage (low numbers are because torch.compile interferes with coverage)

[codecov[bot]]

Codecov Report

Attention: 80 lines in your changes are missing coverage. Please review.

Comparison is base (32ebdfd) 74.73% compared to head (113769c) 73.97%. Report is 1 commits behind head on main.

:exclamation: Current head 113769c differs from pull request most recent head 1ce7b69. Consider uploading reports for the commit 1ce7b69 to get more accurate results

Files	Patch %	Lines
src/gnn_tracking/metrics/losses/oc.py	68.18%	49 Missing :warning:
src/gnn_tracking/metrics/losses/ec.py	62.90%	23 Missing :warning:
src/gnn_tracking/metrics/losses/metric_learning.py	82.14%	5 Missing :warning:
src/gnn_tracking/metrics/losses/__init__.py	93.02%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #455 +/- ## ========================================== - Coverage 74.73% 73.97% -0.77% ========================================== Files 51 54 +3 Lines 3448 3497 +49 ========================================== + Hits 2577 2587 +10 - Misses 871 910 +39 ```

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