fix(player): 修正封面比例与首帧切换闪烁

test/player/player_video_surface_test.dart

@@ -55,9 +55,23 @@ void main() {
     final controller = await _pumpSurface(
       tester,
       openingFrame: const ColoredBox(color: Colors.red),
+      holdOpeningUntilFirstFrame: true,
     );
     expect(_opacity(tester), 0);
 
+    controller.value = const VideoPlayerValue(
+      duration: Duration(minutes: 1),
+      size: Size(1280, 720),
+      position: Duration.zero,
+      isInitialized: true,
+      isPlaying: true,
+    );
+    await tester.pump();
+
+    expect(_opacity(tester), 0);
+    expect(_openingOpacity(tester), 1);
+    expect(find.byKey(const Key('player-opening-frame')), findsOneWidget);
+
     controller.value = const VideoPlayerValue(
       duration: Duration(minutes: 1),
       size: Size(1280, 720),
@@ -153,6 +167,7 @@ Future<VideoPlayerController> _pumpSurface(
   WidgetTester tester, {
   VideoPlayerValue? value,
   Widget? openingFrame,
+  bool holdOpeningUntilFirstFrame = false,
 }) async {
   final controller = VideoPlayerController.networkUrl(
     Uri.parse('http://192.168.31.187:8081/files/video.mp4'),
@@ -167,6 +182,7 @@ Future<VideoPlayerController> _pumpSurface(
           videoUrl: controller.dataSource,
           theater: false,
           openingFrame: openingFrame,
+          holdOpeningUntilFirstFrame: holdOpeningUntilFirstFrame,
         ),
       ),
     ),