feat: merge danmaku

Closes #150

Signed-off-by: bggRGjQaUbCoE <githubaccount56556@proton.me>

lib/utils/extension.dart

@@ -88,3 +88,12 @@ extension BuildContextExt on BuildContext {
     );
   }
 }
+
+extension Unique<E, Id> on List<E> {
+  List<E> unique([Id Function(E element)? id, bool inplace = true]) {
+    final ids = <dynamic>{};
+    var list = inplace ? this : List<E>.from(this);
+    list.retainWhere((x) => ids.add(id != null ? id(x) : x as Id));
+    return list;
+  }
+}