with6<T, A, B, C, D, E, F, R>  static method 
Constructs a StreamTransformer that emits when the source Stream emits, combining
the latest values from all latestFromStreams using the provided function fn.
Implementation
static WithLatestFromStreamTransformer<T, dynamic, R>
    with6<T, A, B, C, D, E, F, R>(
  Stream<A> latestFromStream1,
  Stream<B> latestFromStream2,
  Stream<C> latestFromStream3,
  Stream<D> latestFromStream4,
  Stream<E> latestFromStream5,
  Stream<F> latestFromStream6,
  R Function(T t, A a, B b, C c, D d, E e, F f) fn,
) =>
        WithLatestFromStreamTransformer<T, dynamic, R>(
          [
            latestFromStream1,
            latestFromStream2,
            latestFromStream3,
            latestFromStream4,
            latestFromStream5,
            latestFromStream6,
          ],
          (s, values) {
            return fn(
              s,
              values[0] as A,
              values[1] as B,
              values[2] as C,
              values[3] as D,
              values[4] as E,
              values[5] as F,
            );
          },
        );