Generate UEID for player on connect

[DomonkosSuranyi]

1. Client sends a ConnectionRequest.
2. Server creates a Player entity with UEID additional component.
3. Server sends the UEID to the client as the ConnectionResponse.
4. Client creates an entity with the components: Player, UEID.

UEID should contain a unique u64 ID

[DomonkosSuranyi]

First intuition for implementation:
Server should have an UEIDSupplier resource. It is responsible to generate new UEID-s.
It should store the "highest reserved ID+1" which will be initially 0. When an entity is being deleted that has an UEID, this UEIDSupplier should be notified, because it has to free the deleted UEID.
In this case the freed UEID should be stored in a sorted collection to know that this UEID can be reused.

Downside:
When an entity dies, UEIDSupplier must be manually notified to free its UEID

[DomonkosSuranyi]

no need for ID reuse yet