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/blender_manifest.toml

@@ -12,8 +12,8 @@ platforms = ["windows-x64", "macos-arm64", "linux-x64"]
 license = ["SPDX:GPL-3.0-or-later"]
 
 [permissions]
-network = "Access the local Backend Service and download environment dependencies and model weights"
-files = "Read source images and store runtime data"
+network = "Access the local Service and download environment dependencies and model weights"
+files = "Read source images and store environment data"
 
 [build]
 paths_exclude_pattern = [