docs: def require_valid(self):
          """
          Ensures all tokens are still valid. If expired, attempts to refresh.
          Deletes those which fail to refresh or cannot be refreshed.
          :return: All tokens which are still valid.
          :rtype: :class:`esi.managers.TokenQueryset`
          """
          expired = self.get_expired()
          valid = self.exclude(pk__in=expired)
          valid_expired = expired.bulk_refresh()
          return valid_expired | valid