Expose Temporal Nexus operation info to Temporal Nexus operation

[Quinn-With-Two-Ns]

Expose Temporal Nexus operation info to Temporal Nexus operation.

temporalio/features#673

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Note

Adds a minimal API to retrieve execution context for Nexus Operations.

• Introduces OperationInfo and operationInfo() to access current operation namespace and taskQueue from handler context (context.ts)
• Re-exports operationInfo and OperationInfo from index.ts
• Adds test verifying operationInfo() returns correct namespace and task queue (test-nexus-handler.ts)

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