Reset voice server pinning when a channel becomes empty

Voice channels are automatically pinned to a specific voice server based on the region of the first user who joins. This server remains pinned even after everyone leaves the channel. In international communities, this can cause latency issues. For example, if the first user connects from Europe, users joining later from Asia or Oceania may be routed to a server that is geographically far away from them, even if the channel has been empty in the meantime.

Automatically unpin the voice server when the last user leaves a voice channel, allowing the next user to connect to the nearest available server based on their region.