fix(player): 优化封面过渡与换集起播

test/player/player_opening_frame_test.dart

@@ -83,6 +83,34 @@ void main() {
 
     expect(find.byKey(const Key('player-opening-poster')), findsOneWidget);
   });
+
+  testWidgets('should_reuse_decoded_sprite_when_parent_rebuilds', (
+    tester,
+  ) async {
+    final loader = _FakeSpriteLoader();
+    final cache = OpeningFrameCache();
+    addTearDown(cache.clear);
+    Widget build() => MaterialApp(
+      home: PlayerOpeningFrame(
+        thumbnailsUrl: 'https://cdn.test/thumbnails.vtt',
+        posterUrl: 'https://cdn.test/poster.jpg',
+        loader: loader,
+        cache: cache,
+      ),
+    );
+
+    await tester.pumpWidget(build());
+    await tester.pumpAndSettle();
+    expect(loader.vttCalls, 1);
+    expect(loader.spriteCalls, hasLength(1));
+
+    await tester.pumpWidget(build());
+    await tester.pumpAndSettle();
+
+    expect(loader.vttCalls, 1);
+    expect(loader.spriteCalls, hasLength(1));
+    expect(find.byKey(const Key('player-opening-sprite')), findsOneWidget);
+  });
 }
 
 class _FakeSpriteLoader implements SpriteThumbnailAssetLoader {