Simplify cleaning transformers and shorten module names

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>

classifiers/bow.py

@@ -5,7 +5,7 @@ from sklearn.feature_extraction import DictVectorizer
 from sklearn.linear_model import LogisticRegression
 from sklearn.pipeline import Pipeline
 
-from cleaning.transformers import LowercaseTransformer, PunctuationRemover
+from classifiers.cleaning import LowercaseTransformer, PunctuationRemover
 
 
 class FeatureExtractor:

classifiers/cleaning.py

@@ -1,7 +1,6 @@
 import re
 
 import numpy as np
-from sklearn.base import BaseEstimator, TransformerMixin
 
 
 STOPWORDS = {
@@ -14,18 +13,16 @@ STOPWORDS = {
 }
 
 
-class LowercaseTransformer(BaseEstimator, TransformerMixin):
+class LowercaseTransformer:
     def fit(self, X, y=None):
-        self.fitted_ = True
         return self
 
     def transform(self, X):
         return np.array([msg.lower() for msg in X])
 
 
-class StopwordRemover(BaseEstimator, TransformerMixin):
+class StopwordRemover:
     def fit(self, X, y=None):
-        self.fitted_ = True
         return self
 
     def transform(self, X):
@@ -36,9 +33,8 @@ class StopwordRemover(BaseEstimator, TransformerMixin):
         return " ".join(w for w in words if w.lower() not in STOPWORDS)
 
 
-class PunctuationRemover(BaseEstimator, TransformerMixin):
+class PunctuationRemover:
     def fit(self, X, y=None):
-        self.fitted_ = True
         return self
 
     def transform(self, X):

cli/main.py

@@ -3,7 +3,7 @@
 Usage:
     spam -e
     spam classifiers.manual.ManualClassifier
-    spam classifiers.feature_classifier.FeatureClassifier
+    spam classifiers.features.FeatureClassifier
     spam classifiers.manual.ManualClassifier -t 0.2
     spam classifiers.manual.ManualClassifier -a
     spam classifiers.manual.ManualClassifier -a 5

pyproject.toml

@@ -16,4 +16,4 @@ requires = ["hatchling"]
 build-backend = "hatchling.build"
 
 [tool.hatch.build.targets.wheel]
-packages = ["cli", "classifiers", "cleaning"]
+packages = ["cli", "classifiers"]