feat: Rewindable Actions

[elementbound]

Adds a node that synchronizes events that may or may not happen during specific ticks in the rollback loop. Together with Mutations, it can be used to implement weapon firing fully as part of the rollback loop:

1. Client records input to fire at tick #X
2. Client simulates firing at tick #X, recording the fact with RewindableAction
3. Input arrives at the server
4. Server simulates firing at tick #X, recording the fact with RewindableAction
5. RewindableAction sends a list of ticks where firing was confirmed
6. Client applies changes and resimulates as needed