pause sync when app is backgrounded

lib/controllers/app_paused.dart

@@ -0,0 +1,18 @@
+import "package:flutter/widgets.dart";
+import "package:flutter_riverpod/flutter_riverpod.dart";
+
+class AppPausedController extends Notifier<bool> {
+  @override
+  bool build() {
+    final listener = AppLifecycleListener(
+      onPause: () => state = true,
+      onResume: () => state = false,
+    );
+    ref.onDispose(listener.dispose);
+    return WidgetsBinding.instance.lifecycleState == .paused;
+  }
+
+  static final provider = NotifierProvider<AppPausedController, bool>(
+    AppPausedController.new,
+  );
+}