[Feature Request] [throughputstress] Add Nexus attach-callbacks operation

[prathyushpv]

Is your feature request related to a problem? Please describe.

bench-go's throughput stress test includes a Nexus attach-callbacks step that executes multiple Nexus operations (random count 1-6) concurrently and attaches callbacks. omes does not have an equivalent.

Describe the solution you'd like

Implement a Nexus attach-callbacks action in the throughput stress scenario, similar to bench-go's createNexusOperationAttachCallbacks().

Additional context

Parent tracking issue: #212