Stop units from seeing the post-update versions of other units

[46bit]

RTT's update loop iterates over each player, running an update function on every unit one by one. This means that different units see a different state of the world. Worse it means that some players are at advantage as they see the future positions of their opponents.

I previously experimented with an Entity Component System. I've uploaded that to https://gist.github.com/46bit/aca9571c67c553c7223c1f9f1c61d879. That setup prevents this problem very efficiently, by having two buffers of the same size and alternating them similar to blue-green deploys. So long as RTT uses dynamic state and references (even circular references) this is not so easy.

Unless I really want to adopt an ECS or command-passing architecture, the best thing I can do is to get rid of most of the direct references and refer to things by ID instead. That will simplify cloning.