feat: transfer players to new nodes

[ooliver1]

Summary

This is impressive that it even works.

NodePool.remove_node has been added, which has a transfer_players keyword argument, which:

• False: destroys all players
• True: Player.transfer_to with the best node per player

Player.transfer_to tries its best to:

• Fetch existing player state from old node
• Remove player from internal old node state
• Add player to internal new node state
• Tell the new node about our voice config (endpoint, session id, token)
• Update the new player with track, position, volume, pause, filter

Node.close was also added to disconnect and cleanup an old node, called in NodePool.remove_node

Checklist

• If code changes were made then they have been tested.
• I have run task lint to format code and my changes.
• I have run task pyright and fixed the relevant issues.