Method handle

include/stdexec/coroutine.hpp:159–163

    }

    [[nodiscard]]
    constexpr auto handle() const noexcept -> __std::coroutine_handle<_Promise>
    {
      return STDEXEC::__coroutine_handle_cast<_Promise>(*this);
    }

    [[nodiscard]]
    constexpr operator __std::coroutine_handle<_Promise>() const noexcept