Method get_env

include/exec/sequence/merge_each.hpp:596–599

      using __env_t = decltype(__op_->env_from(__declval<env_of_t<_NestedValueReceiver>>()));
      auto get_env() const noexcept -> __env_t
      {
        return __op_->env_from(STDEXEC::get_env(__nested_value_op_->__rcvr_));
      }
    };

    template <class _NestedValueSender,