Add stream() to generators

[drdamour]

maybe implemented with something like

static Stream<Skugroup> skugroupStream() {
        StreamSupport.stream(
            Spliterators.spliteratorUnknownSize(
                skugroup().iterator(),
                Spliterator.ORDERED
            ),
            false
        )
    }

reason: i write generators in groovy but they are consumed as test jar in many java only projects and getRealized().stream() can be slow