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.

tests/test_manifest.py

@@ -18,7 +18,7 @@ class ManifestTest(unittest.TestCase):
         self.assertEqual(self.manifest["type"], "add-on")
         self.assertNotIn("bl_info", self.manifest)
 
-    def test_declares_required_runtime_permissions(self):
+    def test_declares_required_environment_permissions(self):
         self.assertEqual(
             set(self.manifest["permissions"]),
             {"network", "files"},