Add unit tests for service functionality and model caching

- Implement tests for ben2 and da3 model caching to ensure models are reused for matching runtime keys.
- Verify service state management, including client registration, job cancellation, and client expiration.
- Test discovery file creation and removal based on service ownership.
- Ensure frame extraction functionality works without models and produces expected results.

src/snapform/properties.py

@@ -1,7 +1,7 @@
 import bpy
 
 from .models import gs_model_enum_items, model_enum_items
-from .runtime import device_enum_items
+from .client import device_enum_items
 
 
 class SnapFormSettings(bpy.types.PropertyGroup):