Fix: Ersetzt sleep durch Future.delayed

lib/Controller/background_task_controller.dart

@@ -41,7 +41,7 @@ class BackgroundTaskController {
     final Duration initialDelay,
     final Duration frequency,
   ) async {
-    sleep(initialDelay);
+    await Future.delayed(initialDelay);
 
     final RootIsolateToken? rootIsolateToken = await PortController()
         .getRootIsolateToken();
@@ -51,7 +51,7 @@ class BackgroundTaskController {
       await GenerateTransactionsTask().execute();
     }
 
-    sleep(frequency);
+    await Future.delayed(frequency);
 
     unawaited(_runTask(task, initialDelay, frequency));
   }