set cuda stream?

[NOBLES5E]

It will be useful to set which cuda stream to use in arrayfire, so that we can run kernels in parallel and use external streams to ensure a correct kernel order in some scenarios.

[9prady9]

@NOBLES5E Since this is wrapper to the main project arrayfire, it is not possible to add features that aren't already made available in upstream. There is already an open issue on upstream about the same, please follow it's progress here arrayfire/arrayfire#113 Once the feature is available upstream, it will be made available in the rust wrapper.