Rework rollback tick callbacks

[elementbound]

Background

Regardless of type, tick callbacks are usually called _tick, which can make code more confusing, both to write, read, and to auto-register rollback handlers in RollbackSynchronizer.

Done criteria

1. Rollback tick callback method name is configurable
   1. Defaults to _rollback_tick
2. Code is updated to use new callback name
3. Rollback callback receives an is_fresh flag
   1. True when this is the first time the object simulates the given tick
   2. Can be used for spawning effects, playing sound, etc.

[elementbound]

Removed configurable rollback method name - while it would be cool, I'm too concerned about performance.