Intent of fan-out:_single_partition_handled_locally

All 4 exact tests in this concept. Every test is marked by where it enters the hierarchy.

go.temporal.io/ 4 tests
- server/ 4 tests
  - service/ 4 tests
    
    matching/ 4 tests
    
    TestCancelOutstandingWorkerPolls/ 4 tests
    
    go.temporal.io/server/service/matching/TestCancelOutstandingWorkerPolls/fan-out:_partitions_grouped_by_host Inherited fan-out:_partitions_grouped_by_host
    
    go.temporal.io/server/service/matching/TestCancelOutstandingWorkerPolls/fan-out:_remote_host_error_does_not_block_other_hosts Inherited matching_engine.go ×1
    
    go.temporal.io/server/service/matching/TestCancelOutstandingWorkerPolls/fan-out:_single_partition_handled_locally Introduced here
    
    go.temporal.io/server/service/matching/TestCancelOutstandingWorkerPolls/fan-out:_unimplemented_error_from_old_host_is_handled_gracefully Inherited matching_engine.go ×1