code: def new_uid_validity(cls) -> int:
          
          time_part = int(time.time()) % 4096
          rand_part = random.randint(0, 1048576)
          return (time_part << 20) + rand_part
docs: Generate a new UID validity value for a mailbox, where the first
          two bytes are time-based and the second two bytes are random.