Stabilize versioning3 test helpers

[stephanos]

What changed

• Close standalone versioning3 SDK clients when tests create them.
• Validate speculative task history directly from the poll response.
• Start the sticky completion poll before completing the blocking activity.
• Run versioning3 worker registration pollers until registration is observed, then stop them cleanly.
• Enable the worker service for versioning3 test envs so worker deployment registration APIs have the backing service available.

Verification

• go test -tags test_dep ./tests -run '^TestVersioning3FunctionalSuite$/TestPinnedTask_NoProperPoller/NoTaskForwardNoPollForwardAllowSync$' -count=1 -timeout=10m\n- go test -tags test_dep ./tests -run '^TestVersioning3FunctionalSuite$/TestPinnedQuery_DrainedVersion_PollersAbsent/NoTaskForwardNoPollForwardAllowSync$' -count=1 -timeout=10m\n- go test -tags test_dep ./tests -run '^TestVersioning3FunctionalSuite$/TestPinnedTask_NoProperPoller/NoTaskForwardNoPollForwardAllowSync$|^TestVersioning3FunctionalSuite$/TestPinnedQuery_DrainedVersion_PollersAbsent/NoTaskForwardNoPollForwardAllowSync$' -count=1 -timeout=10m\n- make lint-code

[stephanos]

Starting the final WFT poll before waiting for the activity completion removes an ordering race: under load, completing the activity can immediately unblock and schedule the WFT, and this test should already have the expected poller in place.