Cloud runner does not fetch paginated execution history #510

Problem

The cloud test runner currently calls get_durable_execution_history once when building test results or polling for callbacks. The Lambda history API can return a NextMarker when the event history spans multiple pages, but DurableFunctionCloudTestRunner._fetch_execution_history does not follow that marker.

Impact

Cloud-mode tests can see incomplete execution history for durable executions with enough events to paginate. This can cause missing operations in DurableFunctionTestResult.from_execution_history, incomplete assertions after wait_for_result, and wait_for_callback timeouts when the callback event is on a later page.

Expected behavior

The cloud runner should keep calling get_durable_execution_history with Marker=<previous NextMarker> until the service returns no NextMarker, then merge all events into a single history response for downstream processing.

Reproduction idea

Mock lambda_client.get_durable_execution_history to return multiple pages with NextMarker values and verify the runner requests each page and returns events from all pages.