code: public final Flux<Tuple2<Long, T>> timestamp(Scheduler scheduler) {
  		Objects.requireNonNull(scheduler, "scheduler");
  		return map(d -> Tuples.of(scheduler.now(TimeUnit.MILLISECONDS), d));
  	}
docs: Emit a {@link reactor.util.function.Tuple2} pair of T1 the current clock time in
  millis (as a {@link Long} measured by the provided {@link Scheduler}) and T2
  the emitted data (as a {@code T}), for each item from this {@link Flux}.
  
  <p>
  <img class="marble" src="doc-files/marbles/timestampForFlux.svg" alt="">
  
  @param scheduler the {@link Scheduler} to read time from
  @return a timestamped {@link Flux}