LockstepNetcode: Handle case where state sync arrives early

[rameshvarun]

Right now there's an edge case in LockstepNetcode where the host's authoritative state sync can arrive before a client actually reaches that frame (and thus the client can't apply the state sync). This is mostly likely to happen when communicating over localhost.

The fix is to queue the state syncs if they arrive early.

It should be impossible for a state sync to arrive late since the sync is sent before the host's inputs. Without the host's inputs, we can never advance past that frame.