A method of a linked class annotated with @LinkedTimer(delay, period) is run
repeatedly by the linker, on Spigot and Velocity. The method must not have
parameters, its return value is ignored. It is called through a MethodHandle
bound once when linking instead of reflection; LambdaMetafactory cannot be used
as the linker and the linked classes are in different class loaders.
The unit defaults to ticks and can be set to milliseconds up to hours; the
Unit enum converts it to ticks for Spigot and to a TimeUnit for Velocity.
HullHiderCommand uses it for its tick task.