fix: ios skip posting hash response after detached from engine (#22695)

* skip posting message after detached from engine

* review changes

* cancel plugin before destroying engine

---------

Co-authored-by: shenlong-tanwen <139912620+shalong-tanwen@users.noreply.github.com>
Co-authored-by: Alex <alex.tran1502@gmail.com>

mobile/lib/domain/services/background_worker.service.dart

@@ -192,6 +192,7 @@ class BackgroundWorkerBgService extends BackgroundWorkerFlutterApi {
       _cancellationToken.cancel();
       _logger.info("Cleaning up background worker");
       final cleanupFutures = [
+        nativeSyncApi?.cancelHashing(),
         workerManager.dispose().catchError((_) async {
           // Discard any errors on the dispose call
           return;
@@ -201,7 +202,6 @@ class BackgroundWorkerBgService extends BackgroundWorkerFlutterApi {
         _drift.close(),
         _driftLogger.close(),
         backgroundSyncManager?.cancel(),
-        nativeSyncApi?.cancelHashing(),
       ];
 
       if (_isar.isOpen) {