Function check_task_destruct

tests/BS_thread_pool_test.cpp:2700–2711

* @brief Check that a task is destructed immediately after it executes, and therefore does not artificially extend the lifetime of any captured objects. */

 * @brief Check that a task is destructed immediately after it executes, and therefore does not artificially extend the lifetime of any captured objects.
 */
void check_task_destruct()
{
    constexpr std::chrono::milliseconds sleep_time(20);
    BS::thread_pool pool;
    std::atomic<bool> object_exists = false;
    {
        const std::shared_ptr<detect_destruct> ptr = std::make_shared<detect_destruct>(&object_exists);
        pool.submit_task([ptr] {}).wait();
    }
    std::this_thread::sleep_for(sleep_time);
    check(!object_exists);
}

/**
 * @brief Check that the type trait `BS::common_index_type` works as expected.