fix(mobile): fix stale refs in use timer

The timer hook preserved the values of the original local variables,
which caused issues when hiding controls for videos. The callback can be
changed so that it always sees the latest value with useRef, and it can
be simplified significantly using a function rather than state class.

mobile/lib/utils/hooks/timer_hook.dart

@@ -1,36 +1,17 @@
 import 'package:async/async.dart';
-import 'package:flutter/material.dart';
+import 'package:flutter/foundation.dart';
 import 'package:flutter_hooks/flutter_hooks.dart';
 
-RestartableTimer useTimer(Duration duration, void Function() callback) {
-  return use(_TimerHook(duration: duration, callback: callback));
-}
-
-class _TimerHook extends Hook<RestartableTimer> {
-  final Duration duration;
-  final void Function() callback;
-
-  const _TimerHook({required this.duration, required this.callback});
-  @override
-  HookState<RestartableTimer, Hook<RestartableTimer>> createState() => _TimerHookState();
-}
-
-class _TimerHookState extends HookState<RestartableTimer, _TimerHook> {
-  late RestartableTimer timer;
-  @override
-  void initHook() {
-    super.initHook();
-    timer = RestartableTimer(hook.duration, hook.callback);
-  }
-
-  @override
-  RestartableTimer build(BuildContext context) {
-    return timer;
-  }
-
-  @override
-  void dispose() {
-    timer.cancel();
-    super.dispose();
-  }
+RestartableTimer useTimer(Duration duration, VoidCallback callback) {
+  final latest = useRef(callback);
+  latest.value = callback;
+
+  final timer = useMemoized(
+    () => RestartableTimer(duration, () => latest.value()),
+    [duration],
+  );
+
+  useEffect(() => timer.cancel, [timer]);
+
+  return timer;
 }