Fix ImportanceWeightedScorer compatibility with deep learning models

[YanisLalou]

The ImportanceWeightedScorer was raising a TypeError when used with deep learning models. The error occurred because the scorer was trying to pass the allow_source parameter to the predict_proba method, which is not supported by deep learning models.

Changes:

1. Modified the _score method in the ImportanceWeightedScorer class to handle both scikit-learn estimators and deep learning models.
2. Updated the scorer tests.