Add testing

src/adk_firestore_sessionmanager/firestore_session_service.py

@@ -300,10 +300,8 @@ class FirestoreSessionService(BaseSessionService):
                 )
 
             if state_deltas["session"]:
-                # Use FieldPath to safely update individual state keys
-                # (handles keys that contain dots)
-                field_updates: dict[str | FieldPath, Any] = {
-                    FieldPath("state", k): v
+                field_updates: dict[str, Any] = {
+                    FieldPath("state", k).to_api_repr(): v
                     for k, v in state_deltas["session"].items()
                 }
                 field_updates["last_update_time"] = event.timestamp