Implement sync source-only mode in ServeSession and ChangeBatcher

- Added support for a new sync mode in ServeSession that filters property changes to only include the Source property when the server indicates it is in source-only mode.
- Updated ChangeBatcher to handle the new syncSourceOnly parameter, ensuring that only relevant property changes are processed based on the server's capabilities.
- Enhanced API response to include sync_source_only flag, indicating the server's sync capabilities.
- Adjusted related functions to accommodate the new sync logic, improving data synchronization efficiency.

src/web/api.rs

@@ -95,6 +95,7 @@ impl ApiService {
             place_id: self.serve_session.place_id(),
             game_id: self.serve_session.game_id(),
             root_instance_id,
+            sync_source_only: true,
         })
     }