Array API type hints

[tomwhite]

We should add the Array API type hints to the Cubed implementations. (Suggested by @TomNicholas.)

[lucascolley]

There is a goal to implement proper type hints by the way at https://github.com/data-apis/array-api-typing, see data-apis/array-api#863 for discussion. Work hasn't started on that yet, though.

[tomwhite]

Thanks @lucascolley - I hadn't seen that discussion.