tests(native): subgraph and capture

[romintomasetti]

Summary

This PR further explores graph capture.

We try to get closer to an external library call, wherein some state variables are created and need to be kept alive until the graph is destroyed.

[maartenarnst]

The cuda toolkit documentation says that cudaGraphAddChildGraphNode returns an error if the graph contains memory nodes. This may be an issue with the approach of adding the result of the capture as a child graph node. Probably worth looking into more.

• https://docs.nvidia.com/cuda/cuda-runtime-api/group__CUDART__GRAPH.html#group__CUDART__GRAPH_1g570f14c3186f650206497b6afbb4f499

[romintomasetti]

LGTM.