Implement Standalone Nexus Operations

[VegetarianOrc]

NOTE FOR REVIEWERS: This PR is pending the actual release of the API and Server and will not be merged until those are complete.

I recommend viewing this diff with the histogram diff algorithm to reduce noise and see the additions more clearly. You can view that by checking out the branch and running git diff --histogram origin/main

Add Standalone Nexus Operation Support

API Changes

• Client.create_nexus_client() - Create a typed NexusClient from an endpoint & nexusrpc.Service
• Client.list_nexus_operations() - List operations via visibility query
• Client.count_nexus_operations() - Count operations via visibility query
• Client.get_nexus_operation_handle() - Create a typed NexusOperationHandle to an existing operation
• NexusClient.start_operation() - Start a Nexus Operation and return a NexusOperationHandle.
• NexusClient.execute_operation() - Same as start_operation, but poll the handle for the final result.
• NexusOperationHandle.result() / .describe() / .cancel() / .terminate() / property accessors - interact with an existing operation.
• Supporting types like input types, enums, and errors added as appropriate.

Interceptor Support

The following methods have been added to OutboundInterceptor

• start_nexus_operation()
• describe_nexus_operation()
• cancel_nexus_operation()
• terminate_nexus_operation()
• list_nexus_operations()
• count_nexus_operations()

Testing

Added integration test suite tests/nexus/test_standalone_operations.py (858 lines) covering start, get result, describe, cancel, terminate, list, count, ID conflict/reuse policies, and interceptor integration

Misc Changes

• Update ruff target version to py310 to match the minimum support Python version.

[Evanthx]

Looks pretty good overall!