Move cleaning transformers into classifiers/cleaning.py (dropping the
separate cleaning package) and implement them as plain classes rather
than BaseEstimator/TransformerMixin subclasses, since Pipeline only
needs fit/transform via duck typing. Also rename feature_classifier.py
and bag_of_words.py to features.py and bow.py for brevity.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
bbe8054910