/**
   * Returns a {@link DoubleStream} containing the elements of the first stream, followed by the
   * elements of the second stream, and so on.
   *
   * <p>This is equivalent to {@code Stream.of(streams).flatMapToDouble(stream -> stream)}, but the
   * returned stream may perform better.
   *
   * @see DoubleStream#concat(DoubleStream, DoubleStream)
   */
  public static DoubleStream concat(DoubleStream... streams) {