Allow adding a cudaGraph as a child graph #711

Since the update to 3.10 the capturing functions has been removed. We are now to use (if I understand correctly) either native cuda calls or the cudaStream::begin_capture()+cudaStream::end_capture(). However, these calls returns a new cudaGraph and their is no clear way that I can find in 3.10 to "merge" or incorporate a newly created graph with an existing graph.

So I would like to have a function that looks like:

tf::cudaTask cudaGraph::add_child_graph(cudaGraph);