code: def start(self):
          
          self.broker.emit_before("worker_boot", self)
  
          worker_middleware = _WorkerMiddleware(self)
          self.broker.add_middleware(worker_middleware)
          for _ in range(self.worker_threads):
              self._add_worker()
  
          self.broker.emit_after("worker_boot", self)
docs: Initialize the worker boot sequence and start up all the
          worker threads.