Synchronized execution queue.
Any action can be pushed to this FIFO queue, in order to be executed by Bogue's main loop at the start of the next graphical frame.
For any action that is not super urgent, it is a good idea to use this `Sync` module, instead of launching the action directly from a thread that may be difficult to control. In this way, we ensure that the action is not executed in the middle of rendering the graphics, or between various modifications of the board (events, keyboard focus, etc.).
val push :
(unit -> unit) -> unit
push action registers the
action to be executed by the mainloop at the
start of the next frame, or at a subsequent frame if the queue is already
Warning: the action should not call
Sync.push itself, otherwise this will
result in a deadlock.