Twin RHO Model Step 2: split the training set and train the twin model

[XianzheMa]

Per the title.

The major change is in file modyn/selector/internal/selector_strategies/downsampling_strategies/rho_loss_downsampling_strategy.py

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 96.61017% with 2 lines in your changes missing coverage. Please review.

Project coverage is 82.98%. Comparing base (60d3baa) to head (3e9250a).

Files	Patch %	Lines
...ig/schema/pipeline/sampling/downsampling_config.py	66.66%	1 Missing :warning:
...pling_strategies/rho_loss_downsampling_strategy.py	98.07%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #552 +/- ## ========================================== + Coverage 82.93% 82.98% +0.04% ========================================== Files 221 221 Lines 10306 10342 +36 ========================================== + Hits 8547 8582 +35 - Misses 1759 1760 +1 ```

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[github-actions[bot]]

^{( % to main) ( % to main)}

[MaxiBoether]

Will review when 547 is merged and the branch is updated