Fix start invocation

Author: simolus3

packages/powersync_core/lib/src/sync/streaming_sync.dart

@@ -588,7 +588,13 @@ final class _ActiveRustStreamingIteration {
 
   Future<void> syncIteration() async {
     try {
-      await _control('start', convert.json.encode(sync.options.params));
+      await _control(
+        'start',
+        convert.json.encode({
+          'parameters': sync.options.params,
+          'schema': 'TODO: Pass-through schema (probably in serialized form)',
+        }),
+      );
       assert(_completedStream.isCompleted, 'Should have started streaming');
       await _completedStream.future;
     } finally {