better linting

lib/features/core/utils/mutex.dart

@@ -4,19 +4,19 @@ import 'dart:ui';
 
 /// A simple Mutex implementation using a [Completer].
 class Mutex {
-  final _completerQueue = Queue<Completer>();
+  final _completerQueue = Queue<Completer<void>>();
 
   /// Runs the given [run] function-block in a thread-safe/blocked zone. A convenient `unlock()`
   /// is provided, which can be called anywhere to signal re-entry.
   FutureOr<T> lockAndRun<T>({
     required FutureOr<T> Function(VoidCallback unlock) run,
   }) async {
-    final completer = Completer();
+    final completer = Completer<void>();
     _completerQueue.add(completer);
     if (_completerQueue.first != completer) {
       await _completerQueue.removeFirst().future;
     }
-    final value = await run(() => completer.complete());
+    final value = await run(completer.complete);
     return value;
   }