fix(player): 完善进度预览清屏与下拉刷新

lib/core/data/services/sprite_thumbnail_axis.dart

@@ -122,6 +122,8 @@ abstract interface class SpriteThumbnailAxisSource implements Listenable {
   SpriteThumbnailFrame? cachedFrameAt(String? thumbnailsUrl, Duration position);
 
   bool hasAxis(String? thumbnailsUrl);
+
+  Future<void> prepareAt(String? thumbnailsUrl, Duration position);
 }
 
 /// VTT 时间轴、cue 二分与 sprite ui.Image LRU 缓存。
@@ -153,6 +155,7 @@ class SpriteThumbnailAxisService extends ChangeNotifier
   List<String> get spriteCacheKeys => _spriteCache.keys.toList();
 
   /// 播放器就绪时预取当前 cue 与相邻 sprite，拖动帧不触发网络或解码。
+  @override
   Future<void> prepareAt(String? thumbnailsUrl, Duration position) async {
     final url = _normalizeUrl(thumbnailsUrl);
     if (_disposed || url == null) return;