Async functions should go beyond a single node

[zohimchandani]

Required prerequisites

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Describe the feature

observe_async can be used with the mqpu backend.

If I am on a cluster with 2 nodes and 4 gpus per node, my target.num_qpus() = 4 but cudaq.mpi.num_ranks() = 8.

I would now like to execute observe_async(kernel, hamiltonian, qpu_id = 7) however the error is that qpu_id must be <= target.num_qpus()

Can we get all async functions to work beyond a node, please?

Thanks.