Method visualize

example/sem.cpp:56–69

    }

    task<void> visualize(unsigned id, unsigned x_scale = 2) const {
        auto cout_n = [=](auto str, unsigned n) {
            n *= x_scale;
            while (n-- > 0) {
                std::cout << str;
            }
        };
        auto guard = co_await cout_mutex.lock_guard();
        std::cout << "#" << std::setw(2) << id << " ";
        cout_n("░", delay);
        cout_n("▒", wait_on_sema);
        cout_n("█", occupy);
        std::cout << '\n';
    }

    static void show_info() {
        std::cout