Remove reliance on socketIds

[richpjames]

According to the Socket.IO docs we shouldn't use a socket's ID for anything other than debugging.
We currently use it as a unique identifier for a client.
There's more information here: https://socket.io/docs/v4/server-api/#socketid

There's an example of where we could go with this here: https://github.com/socketio/socket.io/tree/main/examples/private-messaging
But it looks relatively complicated to me so maybe there is a simpler route we can take

[yndajas]

Could we just create a separate ID in the server when a player joins, and return that ID to the socket that joined (without using its socket ID), which it can then pass instead of the socket ID with any future events?

[yndajas]

Although setting it in a cookie might be more disconnect/refresh-proof, which would make things more user-friendly! But it might allow users to change their ID to someone else's...