code: public final Flux<Tuple2<Long, T>> elapsed(Scheduler scheduler) {
  		Objects.requireNonNull(scheduler, "scheduler");
  		return onAssembly(new FluxElapsed<>(this, scheduler));
  	}
docs: Map this {@link Flux} into {@link reactor.util.function.Tuple2 Tuple2&lt;Long, T&gt;}
  of timemillis and source data. The timemillis corresponds to the elapsed time
  between each signal as measured by the provided {@link Scheduler}.
  First duration is measured between the subscription and the first element.
  <p>
  <img class="marble" src="doc-files/marbles/elapsedForFlux.svg" alt="">
  
  @param scheduler a {@link Scheduler} instance to {@link Scheduler#now(TimeUnit) read time from}
  
  @return a new {@link Flux} that emits tuples of time elapsed in milliseconds and matching data