optimizations

mobile/lib/utils/async_mutex.dart

@@ -5,7 +5,7 @@ class AsyncMutex {
   Future _running = Future.value(null);
   int _enqueued = 0;
 
-  get enqueued => _enqueued;
+  int get enqueued => _enqueued;
 
   /// Execute [operation] exclusively, after any currently running operations.
   /// Returns a [Future] with the result of the [operation].

mobile/lib/utils/debounce.dart

@@ -27,8 +27,9 @@ class Debouncer {
   }
 
   Future<void>? drain() {
-    if (_timer != null && _timer!.isActive) {
-      _timer!.cancel();
+    final timer = _timer;
+    if (timer != null && timer.isActive) {
+      timer.cancel();
       if (_lastAction != null) {
         _callAndRest();
       }