class Async::Deadline

@returns [Numeric] The remaining time (may be negative if expired).
the remaining time by the elapsed duration since the last call.
Each call to this method advances the internal clock and reduces
Get the remaining time, updating internal state.

def remaining
	now = Clock.now
	delta = now - @start
	@start = now
	
	@remaining -= delta
	
	return @remaining
end