docs: def _kill(self) -> None:
          """
          Hard kill.
          
          - PROBLEM: originally, via ``self.process.kill()``, could leave orphans
            under Windows.
          - SOLUTION: see
            https://stackoverflow.com/questions/1230669/subprocess-deleting-child-processes-in-windows,
            which uses ``psutil``.
  
          """  # noqa
          self.warning("Using a recursive hard kill; will assume it worked")
          pid = self.process.pid
          gone, still_alive = kill_proc_tree(pid, including_parent=True,
                                             timeout_s=self.kill_timeout_sec)
          self.debug("Killed: {!r}".format(gone))
          self.warning("Still alive: {!r}".format(still_alive))