Update message acks cleanup #130
Description
The manual fragmentation PR #116 changes how component updates are acked. The server tracks pending acks, and removes them when an ack appears. This is currently a memory leak since the client isn't guaranteed (or expected) to ack all component updates, which are sent over an unreliable channel.
We should add a cleanup protocol that automatically discards stale pending acks after a period of time (e.g. 2x the server's client timeout).