[jmaeagle99]

What changed?

Added WorkflowWorkerCompletionPaginationTest, which runs one workflow task through a real WorkflowWorker with a mocked service and checks every RespondWorkflowTaskCompleted request:

• Intermediate pages are sent in order, all sharing the task token, before the final page. The final page carries the messages and no commands.
• When the namespace doesn't support pagination, the completion is sent as one request.
• Buffer loss on the final page, or on an intermediate page, resends every page from page 0.
• Other errors (NOT_FOUND for a stale token) are not resent.
• Worker shutdown ends the buffer-loss resend loop.
• Each attempt sends a lost-buffer page exactly once, so the gRPC retryer never retries it on its
  own.

The harness waits until the task's slot is released before shutting the worker down, because shutdown ends the resend loop early.

Why?

The existing tests covered only WorkflowTaskCompletionPaginator.paginate(). The send and resend logic in WorkflowWorker had no unit coverage, which is how the bug fixed in #3177 shipped. The integration test enabled by that PR covers only the success path.

Checklist

1. How this was tested: Each test was checked against a deliberately broken send loop, and each one failed.

2. Any docs updates needed? No, test only.