code: public <U> FutureStream<U> constructFutures(final Stream<CompletableFuture<U>> s) {
          final LazyReact toUse = withStreamOfFutures(true);
          return toUse.construct((Stream<U>) s);
      }
docs: Construct a FutureStream from a Stream of CompletableFutures
  
  @param s Stream of CompletableFutures
  @return FutureStream