Consider input validation to loss functions

[asmith26]

We have currently/intentionally not added input validation and exception raising to loss functions to prevent potential performance loss. It could be beneficial to explore mechanisms (e.g. potentially via python decorators) for adding this.

Validations suggestions:

• test_raises_error_when_any_y_true_and_y_pred_lengths_different
• For losses that expect a probability input (between 0 and 1).
  • test_raises_error_when_y_true_not_sum_1
  • test_raises_error_when_y_pred_not_sum_1
  • test_raises_error_when_any_y_pred_le_0
  • test_raises_error_when_any_y_pred_gt_1