feat: add playback seeking

tests/fakes.py

@@ -59,9 +59,11 @@ def build_player(default_plays: int = 5) -> tuple[MusicPlayer, FakeVoiceClient]:
     bot.loop = asyncio.get_event_loop()
     voice_client = FakeVoiceClient()
 
-    async def recreate(track, loop=None):
+    async def recreate(track, loop=None, start_at=0.0):
         fresh = FakeTrack(track.id)
         fresh.plays_left = track.plays_left
+        fresh.duration = track.duration
+        fresh.elapsed = start_at
         return fresh
 
     tracks = MagicMock()