chore: refactor _lexicons.py

Author: fin-griffin

src/voice/stylometry/_function_words.py src/voice/stylometry/_lexicons.pysrc/voice/stylometry/_function_words.py renamed to src/voice/stylometry/_lexicons.py

@@ -1,14 +1,13 @@
 """
-Canonical English function word lexicon.
+Internal lexicons used by stylometric metrics.
 
-Source: NLTK cf. https://gist.github.com/sebleier/554280
-
-Notes:
-- Lowercase only
+This package contains private lexicon data that are not part of the public API.
 """
 
 from __future__ import annotations
 
+# Canonical English function word lexicon (lowercase only)
+# Source: NLTK cf. https://gist.github.com/sebleier/554280
 FUNCTION_WORDS: frozenset[str] = frozenset(
     {
         "i",

src/voice/stylometry/metrics.py

@@ -30,7 +30,7 @@
 from dataclasses import dataclass
 
 from voice.stylometry._defaults import PARAMETER_DEFAULTS
-from voice.stylometry._function_words import FUNCTION_WORDS
+from voice.stylometry._lexicons import FUNCTION_WORDS
 from voice.stylometry._sequence_stats import (
     length_central_moment_from_units,
     mattr_from_units,