Method occupy_sema

example/sem.cpp:44–54

    task<void> initial_delay() const { co_await timeout(delay * time_tick); }

    task<void> occupy_sema() {
        wait_on_sema = static_cast<unsigned>(
            std::chrono::duration_cast<std::chrono::milliseconds>(
                std::chrono::high_resolution_clock::now() - started_at
                - delay * time_tick
            )
                .count()
            / time_tick.count()
        );
        co_await timeout(occupy * time_tick);
    }

    task<void> visualize(unsigned id, unsigned x_scale = 2) const {
        auto cout_n = [=](auto str, unsigned n) {