Function set_stopped

include/exec/static_thread_pool.hpp:1527–1531

      }

      void set_stopped() noexcept
      {
        shared_state& state = shared_state_;
        STDEXEC::set_stopped(static_cast<Receiver&&>(state.rcvr_));
      }

      auto get_env() const noexcept -> env_of_t<Receiver>
      {