[ptbench.engine] Simplified, documented and created type hints for the ``callbacks`` module; Added type hints to the resource module

[ptbench.data.datamodule] Implemented typing, added more logging, implemented sampler-balancing depending on sample class prevalence, parallelized dataset caching

Implemented BCEWithLogitsLoss reweighting function
Removed save_hyperparameters from model
Apply augmentation transforms on singular images
Fixed model summary

[datamodule] Slightly streamlines the datamodule approach; adds documentation; adds type annotations; adds TODOs

Relevance analysis has been moved out of predict.py and into a separate
script. It is not currently functional.