feat: add OmniVoiceModelLoader node

Implements OmniVoiceModelLoader with INPUT_TYPES, RETURN_TYPES, and
load_model supporting both HuggingFace auto-download and local path
sources. Adds TDD test suite and pytest infrastructure (conftest.py,
pytest.ini) to enable testing outside ComfyUI without omnivoice installed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

__init__.py

@@ -1,13 +1,18 @@
-from .nodes import OmniVoiceModelLoader, OmniVoiceGenerate
+try:
+    from .nodes import OmniVoiceModelLoader, OmniVoiceGenerate
 
-NODE_CLASS_MAPPINGS = {
-    "OmniVoiceModelLoader": OmniVoiceModelLoader,
-    "OmniVoiceGenerate": OmniVoiceGenerate,
-}
+    NODE_CLASS_MAPPINGS = {
+        "OmniVoiceModelLoader": OmniVoiceModelLoader,
+        "OmniVoiceGenerate": OmniVoiceGenerate,
+    }
 
-NODE_DISPLAY_NAME_MAPPINGS = {
-    "OmniVoiceModelLoader": "OmniVoice Model Loader",
-    "OmniVoiceGenerate": "OmniVoice Generate",
-}
+    NODE_DISPLAY_NAME_MAPPINGS = {
+        "OmniVoiceModelLoader": "OmniVoice Model Loader",
+        "OmniVoiceGenerate": "OmniVoice Generate",
+    }
+except ImportError:
+    # Graceful fallback when loaded outside of a package context (e.g. pytest)
+    NODE_CLASS_MAPPINGS = {}
+    NODE_DISPLAY_NAME_MAPPINGS = {}
 
 __all__ = ["NODE_CLASS_MAPPINGS", "NODE_DISPLAY_NAME_MAPPINGS"]