Add support for Stand Alone Nexus Operations

[Quinn-With-Two-Ns]

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

Summary

• Adds stand-alone Nexus operation support, allowing Nexus operations to be started, managed, and queried directly from the client
  (outside of workflows)
• Updates sdk-core submodule to stand-alone-nexus-operations branch and regenerates proto bindings (8 new RPCs)
• Introduces NexusClient / NexusClient with both string-based and expression-based operation invocation, mirroring the existing
  NexusWorkflowClient pattern

API Surface

On ITemporalClient:

• CreateNexusClient(service, options) / CreateNexusClient(options) — factory methods
• GetNexusOperationHandle(operationId, runId?) — handle for existing operations
• ListNexusOperationsAsync(query) / CountNexusOperationsAsync(query) — visibility queries

On NexusClient:

• StartNexusOperationAsync / ExecuteNexusOperationAsync — start or start+await operations

On NexusOperationHandle:

• GetResultAsync — polls PollNexusOperationExecution until completion
• DescribeAsync / CancelAsync / TerminateAsync

All operations flow through the ClientOutboundInterceptor chain, consistent with stand-alone activities.

Test plan

• Existing Nexus worker tests pass (30/30 verified)
• Build succeeds with 0 errors across all target frameworks
• Integration tests for start, get result, describe, cancel, terminate, list, count
• Verify expression-based invocation with NexusClient
• Verify NexusOperationAlreadyStartedException on ID conflict

---

Note

Medium Risk
Medium risk due to regenerated protobuf bindings and new enums/messages that expand public API surface; consumers may see compile-time warnings (new [Obsolete] fields) and behavior changes when serializing/deserializing new fields.

Overview
Adds new protobuf API surface to support standalone Nexus operations and worker compute configuration.

This regenerates protocol bindings to introduce Temporalio.Api.Compute.V1 (ComputeConfig, ComputeProvider, ComputeScaler), extends deployment/version protos to carry compute_config plus last_modifier_identity, and adds Nexus-related enums and error details (e.g., NexusOperationExecutionAlreadyStartedFailure). It also extends common protos with a new Link variant for nexus_operation and introduces a server-derived Principal message.

Separately, marks several command namespace fields as [Obsolete] due to cross-namespace deprecation, adds new event/worker-deployment status enum values, and updates OpenTelemetry TracingInterceptor to use the fully-qualified StartNexusOperationInput type.

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