duplicateClip method
Inserts a copy of clip index right after it.
Implementation
void duplicateClip(int index) {
if (index < 0 || index >= clips.length) return;
final source = clips[index];
final copy = source.copyWith(
id: '${source.id}_copy_${DateTime.now().microsecondsSinceEpoch}',
clearConvertedVideoFile: true,
);
clipController.insertClip(index + 1, copy);
_activeTrack = VideoTrackType.clip;
_saveState();
notifyListeners();
}