docs: def timedelta_isoformat(td: datetime.timedelta) -> str:
      """
      ISO 8601 encoding for timedeltas.
      """
      minutes, seconds = divmod(td.seconds, 60)
      hours, minutes = divmod(minutes, 60)
      return f'P{td.days}DT{hours:d}H{minutes:d}M{seconds:d}.{td.microseconds:06d}S'