- now workers passes queue to task_executor so it can send back events per item and on retry attempt
- updated result class to pass along events to strategy
- base strategy updated to forward new events to callback
- callbacks now remove 'items' on final result but process them directly when invoked per item
- new callback method to deal with retry attempt messages (also now obeys nolog)
- updated tests to match new signature of task_executor
fixes#14558fixes#14072