On each tick, Paper runs EntityScheduler's executeTick of each entity. This is a bit expensive, due to ArrayDeque's size() call because it ain't a simple "get the current queue size" function, and due to the thread checks.
To avoid the hefty ArrayDeque's size() call, we check if we *really* need to execute the executeTick, by checking if currentlyExecuting is not empty or if oneTimeDelayed is not empty.
Most entities won't have any scheduled tasks, so this is a nice performance bonus. These optimizations, however, wouldn't work in a Folia environment, but because in SparklyPaper executeTick is always executed on the main thread, it ain't an issue for us (yay).
