Method request_stop

include/exec/sequence/merge_each.hpp:126–133

      }

      bool request_stop() noexcept
      {
        if constexpr (!unstoppable_token<__stop_token_t>)
        {
          return __stop_source_.request_stop();
        }
        return false;
      }

      inplace_stop_token get_token() const & noexcept
      {