fix(player): 预热直出并与视频统一封面布局

lib/core/data/services/playback_session.dart

@@ -260,6 +260,7 @@ class PlaybackSession extends ChangeNotifier {
           _usableWarm(this, warmNext, index) ??
           _usableWarm(this, warmPrevious, index);
       if (warm != null) {
+        warm.reusedWarm = true;
         target = _active = warm;
         _loading = !warm.prepared;
         _notify();
@@ -470,5 +471,6 @@ class _PlayerSlot {
   bool activated = false;
   bool playing = false;
   bool retiring = false;
+  bool reusedWarm = false;
   Object? failure;
 }

lib/core/data/services/playback_session_controls.dart

@@ -19,6 +19,16 @@ extension PlaybackSessionControls on PlaybackSession {
     return slot.player;
   }
 
+  /// 当前索引是否复用了已预热的播放器槽。
+  bool reusedWarmAt(int index) {
+    for (final slot in [_active, _next, _previous]) {
+      if (slot != null && !slot.retiring && slot.index == index) {
+        return slot.reusedWarm;
+      }
+    }
+    return false;
+  }
+
   /// 同步应用前台状态并恢复或暂停当前集。
   void setAppResumed(bool value) {
     _appResumed = value;