…stic#130279)

When a search targets a single shard, the fetch phase is executed in the same roundtrip as the query phase. In that case the search context is reused across phases, and the cancellation runnables registered to the searcher are reused. This is incorrect as the search timeout check should not be applied to the fetch phase, or it will make fetching partial results unfeasible. For instance if the query phase times out, the fetch phase will time out as well and there won't be partial results. If the query phase does not time out, but the fetch phase does, the latter will return a different set of results compared to those expected which will lead to unexpected situations like an array index out of bound exception.

This commit clears the cancellation runnables ahead of running the fetch phase in the same rountrip as query and performs their registration once again, without the timeout checks which are never applied to the fetch phase.

Closes elastic#130071