def _finalize_step(self):
        """Finalize simulation step after all agents have acted for the current
        step.
        """
        t = time.time()
        if self._callback is not None:
            self._callback(self.age)
        t2 = time.time()
        self._step_processing_time += t2 - t
        self._log(logging.INFO, "Step {} run in: {:.3f}s ({:.3f}s of "
                  "actual processing time used)"
                  .format(self.age, self._step_processing_time,
                          t2 - self._step_start_time))
        self._processing_time += self._step_processing_time
Finalize simulation step after all agents have acted for the current
        step.