Tkurth/improved state handling

[azrael417]

This branch will contain some major refactoring of preprocessor.py and noise.py. Those two rely on some states with implicitly assumptions and for some features implement order contracts. This MR will clean up all of this because it can lead to semantic problems and data corruption if not aware.

• rewrites noise.py and preprocessor.py to not accidentally hold on to dead references
• folds local ensemble dimension into batch dimension for forward pass, simplifies a lot of the noise handling
• added more data loader tests related to number of samples in epochs and cycles.
• added external source fix for split file DALI loader which silently duplicated samples. Invalid samples are excluded from the file list now

Do not merge before #77