Function get_env

include/exec/sequence/merge_each.hpp:1061–1064

      using __env_t = typename _OperationBase::__nested_stop_env_t;
      auto get_env() const noexcept -> __env_t
      {
        return __op_->__nested_stop_.env_from(__op_->__rcvr_);
      }
    };

    template <class _NestedSequenceSender,