code: public static <T> void onTimeout(CompletableFuture<T> future, Consumer<TimeoutException> callback) {
          exceptionListener(future, TimeoutException.class, callback);
      }
docs: Attaches the given callback as an exception listener to the given CompletableFuture, which will be invoked when
  the future times out (fails with a TimeoutException).
  
  @param future   The future to attach to.
  @param callback The callback to invoke.
  @param <T>      The Type of the future's result.