docs: public int removeTimer(Object arg)
      {
          Objects.requireNonNull(arg, "Argument has to be supplied");
  
          //  We cannot touch self->timers because we may be executing that
          //  from inside the poll loop. So, we hold the arg on the zombie
          //  list, and process that list when we're done executing timers.
          zombies.add(arg);
          if (verbose) {
              System.out.printf("I: zloop: cancel timer\n");
          }
  
          return 0;
      }