fix(mobile): video state (#26574)

Consolidate video state into a single asset-scoped provider, and reduce
dependency on global state generally. Overall this should fix a few
timing issues and race conditions with videos specifically, and make
future changes in this area easier.

mobile/lib/utils/hooks/interval_hook.dart

@@ -1,15 +0,0 @@
-import 'dart:async';
-import 'dart:ui';
-
-import 'package:flutter_hooks/flutter_hooks.dart';
-
-// https://github.com/rrousselGit/flutter_hooks/issues/233#issuecomment-840416638
-void useInterval(Duration delay, VoidCallback callback) {
-  final savedCallback = useRef(callback);
-  savedCallback.value = callback;
-
-  useEffect(() {
-    final timer = Timer.periodic(delay, (_) => savedCallback.value());
-    return timer.cancel;
-  }, [delay]);
-}