refactor: move backend implementations to tts_backends package

Moved SupertonicPipeline from abogen/tts_supertonic.py to
abogen/tts_backends/supertonic.py and load_numpy_kpipeline from
abogen/utils.py to abogen/tts_backends/kokoro.py.

Git correctly detects the Supertonic file as a rename (R),
preserving full commit history.

- New package: abogen/tts_backends/
  - __init__.py (package marker)
  - supertonic.py (SupertonicPipeline, moved from tts_supertonic.py)
  - kokoro.py (load_numpy_kpipeline, moved from utils.py)
- abogen/utils.py: re-exports load_numpy_kpipeline for backward compat
- All imports updated to new canonical paths

abogen/tts_backends/kokoro.py

@@ -0,0 +1,5 @@
+def load_numpy_kpipeline():
+    import numpy as np
+    from kokoro import KPipeline  # type: ignore[import-not-found]
+
+    return np, KPipeline

abogen/utils.py

@@ -529,13 +529,6 @@ def prevent_sleep_end():
                 _sleep_procs[system] = None
 
 
-def load_numpy_kpipeline():
-    import numpy as np
-    from kokoro import KPipeline  # type: ignore[import-not-found]
-
-    return np, KPipeline
-
-
 class LoadPipelineThread(Thread):
     def __init__(self, callback):
         super().__init__()
@@ -543,6 +536,8 @@ class LoadPipelineThread(Thread):
 
     def run(self):
         try:
+            from abogen.tts_backends.kokoro import load_numpy_kpipeline
+
             np_module, kpipeline_class = load_numpy_kpipeline()
             self.callback(np_module, kpipeline_class, None)
         except Exception as e:

abogen/voice_profiles.py

@@ -3,7 +3,7 @@ import os
 from typing import Any, Dict, Iterable, List, Tuple
 
 from abogen.constants import VOICES_INTERNAL
-from abogen.tts_supertonic import DEFAULT_SUPERTONIC_VOICES
+from abogen.tts_backends.supertonic import DEFAULT_SUPERTONIC_VOICES
 from abogen.utils import get_user_config_path
 
 

abogen/webui/conversion_runner.py

@@ -39,15 +39,15 @@ from abogen.utils import (
     get_user_cache_path,
     get_user_output_path,
     load_config,
-    load_numpy_kpipeline,
 )
+from abogen.tts_backends.kokoro import load_numpy_kpipeline
 from abogen.tts_backend import TTSBackend
 from abogen.voice_cache import ensure_voice_assets
 from abogen.voice_formulas import extract_voice_ids, get_new_voice
 from abogen.voice_profiles import load_profiles, normalize_profile_entry
 from abogen.pronunciation_store import increment_usage
 from abogen.llm_client import LLMClientError
-from abogen.tts_supertonic import DEFAULT_SUPERTONIC_VOICES, SupertonicPipeline
+from abogen.tts_backends.supertonic import DEFAULT_SUPERTONIC_VOICES, SupertonicPipeline
 
 from .service import Job, JobStatus
 

abogen/webui/debug_tts_runner.py

@@ -15,7 +15,7 @@ from abogen.normalization_settings import build_apostrophe_config
 from abogen.text_extractor import extract_from_path
 from abogen.voice_cache import ensure_voice_assets
 from abogen.webui.conversion_runner import SAMPLE_RATE, SPLIT_PATTERN, _select_device, _to_float32, _resolve_voice, _spec_to_voice_ids
-from abogen.utils import load_numpy_kpipeline
+from abogen.tts_backends.kokoro import load_numpy_kpipeline
 
 
 _MARKER_RE = re.compile(re.escape(MARKER_PREFIX) + r"(?P<code>[A-Z0-9_]+)" + re.escape(MARKER_SUFFIX))

abogen/webui/routes/utils/preview.py

@@ -78,7 +78,7 @@ def get_preview_pipeline(language: str, device: str) -> Any:
         pipeline = _preview_pipelines.get(key)
         if pipeline is not None:
             return pipeline
-        from abogen.utils import load_numpy_kpipeline
+        from abogen.tts_backends.kokoro import load_numpy_kpipeline
 
         _, KPipeline = load_numpy_kpipeline()
         pipeline = KPipeline(lang_code=language, repo_id="hexgrad/Kokoro-82M", device=device)
@@ -137,7 +137,7 @@ def generate_preview_audio(
             normalized_text = source_text
 
     if provider == "supertonic":
-        from abogen.tts_supertonic import SupertonicPipeline
+        from abogen.tts_backends.supertonic import SupertonicPipeline
 
         pipeline = SupertonicPipeline(sample_rate=SAMPLE_RATE, auto_download=True, total_steps=supertonic_total_steps)
         segments = pipeline(

abogen/webui/routes/utils/voice.py

@@ -20,7 +20,7 @@ from abogen.constants import (
     VOICES_INTERNAL,
 )
 from abogen.speaker_configs import list_configs
-from abogen.utils import load_numpy_kpipeline
+from abogen.tts_backends.kokoro import load_numpy_kpipeline
 from abogen.webui.conversion_runner import _select_device, _to_float32, SAMPLE_RATE, SPLIT_PATTERN
 
 _preview_pipeline_lock = threading.RLock()

tests/test_preview_applies_manual_overrides.py

@@ -32,7 +32,7 @@ def test_preview_applies_manual_override_before_normalization(monkeypatch):
 
     monkeypatch.setitem(
         __import__("sys").modules,
-        "abogen.tts_supertonic",
+        "abogen.tts_backends.supertonic",
         type("M", (), {"SupertonicPipeline": DummyPipeline}),
     )
 

tests/test_tts_supertonic_unsupported_chars.py

@@ -1,6 +1,6 @@
 import numpy as np
 
-from abogen.tts_supertonic import SupertonicPipeline
+from abogen.tts_backends.supertonic import SupertonicPipeline
 
 
 class _DummyTTS:

tests/test_voice_formula_resolution.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 from abogen.webui.conversion_runner import _resolve_voice, _supertonic_voice_from_spec
-from abogen.tts_supertonic import DEFAULT_SUPERTONIC_VOICES
+from abogen.tts_backends.supertonic import DEFAULT_SUPERTONIC_VOICES
 
 
 def test_resolve_voice_formula_without_pipeline_does_not_crash() -> None: