[Bug] Cross validation yields unexpected additional info

[nabenabe0928]

Issue Description

It seems abstract evaluator does not save cross-validated performance for opt/test datasets.
Also train_evaluator.py is too messy and requires major refactoring.

Possible Solution

Modify calculate_auxiliary_losses in abstract_evaluator.py

Your Code

When using the new results_manager, the following yields the issue.
(Although I fixed it)

python -m pytest test/test_api/test_api.py::test_tabular_classification[CrossValTypes.k_fold_cross_validation-resampling_strategy_args1-40981] -W ignore