fix(player): 使用雪碧图预热首帧兜底

test/playback/seek_progress_bar_test.dart

@@ -249,9 +249,7 @@ void main() {
     },
   );
 
-  testWidgets('should_show_frame_card_with_cover_then_hide_on_release', (
-    tester,
-  ) async {
+  testWidgets('should_show_frame_card_then_hide_on_release', (tester) async {
     final video = ValueNotifier<VideoPlayerValue>(
       const VideoPlayerValue(
         duration: Duration(seconds: 12),
@@ -272,7 +270,6 @@ void main() {
                 valueListenable: video,
                 semanticsLabel: 'Seek video',
                 episodeId: 'episode-1',
-                posterUrl: '',
                 thumbnailService: service,
                 onSeek: (_) async {},
               ),
@@ -289,7 +286,7 @@ void main() {
     await tester.pump();
 
     expect(find.byKey(const Key('scrub-preview-card')), findsOneWidget);
-    expect(find.byKey(const Key('scrub-preview-poster')), findsOneWidget);
+    expect(find.byKey(const Key('scrub-preview-background')), findsOneWidget);
     expect(find.byKey(const Key('scrub-preview-frame')), findsNothing);
     expect(find.textContaining('/ 00:12'), findsOneWidget);
     expect(