Add workflow signal-with-start feature coverage

[tconley1428]

Summary

Adds end-to-end System Nexus Signal-with-Start-from-workflow coverage on top of the design document.

• Pins the dev server used by feature runs to CLI v1.8.3-server-1.32.0-162.0, which supports the required dynamic configuration.
• Adds a dynamic-config variant enabling history.enableSignalWithStartFromWorkflow.
• Covers the basic start-then-use-existing flow in Python and .NET.
• Adds a separate advanced execution that verifies Signal-with-Start inner payloads use the target workflow serialization context and traverse the configured converter/codec. Python additionally verifies external-storage handling.

Validation

• Basic .NET end-to-end execution passes against the pinned dev server.
• The advanced .NET assertions currently expose an SDK gap: inner payload conversion receives the caller workflow context and the codec has no System Nexus context. The feature intentionally retains the strict target-context assertions; the corresponding SDK support is needed before the full .NET feature passes.
• Python advanced coverage passes against the SDK fix in temporalio/sdk-python#1825.