code: @NotNull
      public IntStream map(@NotNull final IntUnaryOperator mapper) {
          return new IntStream(params, new IntMap(iterator, mapper));
      }
docs: Returns an {@code IntStream} consisting of the results of applying the given
  function to the elements of this stream.
  
  <p> This is an intermediate operation.
  
  <p>Example:
  <pre>
  mapper: (a) -&gt; a + 5
  stream: [1, 2, 3, 4]
  result: [6, 7, 8, 9]
  </pre>
  
  @param mapper a non-interfering stateless function to apply to
  each element
  @return the new {@code IntStream}