[atol]

What was changed

• Signals and signal-with-start sent through TemporalNexusClient.client in a Temporal operation handler now reuse the Nexus operation's request ID.
• Breaking (experimental API): each handler run can send only one such signal; a second raises a BAD_REQUEST nexusrpc.HandlerError. (Signal-with-start counts toward the limit; a failed signal doesn't; a retried Nexus task starts with a fresh limit.)
• Signals sent through temporalio.nexus.client() are unchanged.
• Based on De-duplicate Nexus Signal and SignalWithStart operations sdk-go#2781.

Why?

When a Nexus task is retried, the handler reruns and sends its signal again with a new random request ID, so the workflow receives it twice. Reusing the operation's request ID lets the server dedupe the retry. However, every signal in one handler run then shares that ID, so a second signal to the same workflow would be silently dropped while reported as delivered. Limiting each run to one signal turns that silent loss into a clear error.

Checklist

1. How was this tested:
   Added integration tests.

2. Any docs updates needed?
   No.