Enhance syncback process by integrating serialization of service children

- Introduced `SerializationService` to serialize child instances during syncback, improving data handling.
- Updated `performSyncback` to include serialized children data in the syncback request.
- Refactored `ServiceChunk` structure to store child count instead of serialized data, optimizing memory usage.
- Adjusted related functions and tests to accommodate the new data structure, ensuring consistency and accuracy in syncback operations.

These changes significantly enhance the efficiency and clarity of the syncback process, allowing for better management of service data.

src/web/api.rs

@@ -247,11 +247,13 @@ async fn handle_api_syncback(
     }
 
     log::info!(
-        "Live syncback requested with {} service chunks",
-        syncback_request.services.len()
+        "Live syncback requested with {} service chunks, {} bytes of rbxm data",
+        syncback_request.services.len(),
+        syncback_request.data.len()
     );
 
     let payload = SyncbackPayload {
+        data: syncback_request.data,
         services: syncback_request.services,
     };
     syncback_signal.fire(payload);