Function delayed_reject

tests/fl/task/executor.cpp:629–642

// Helper: Create a promise that rejects after a delay
template<typename T>
fl::task::Promise<T> delayed_reject(const fl::task::Error& error, uint32_t delay_ms) {
    auto p = fl::task::Promise<T>::create();

    fl::thread t([p, error, delay_ms]() mutable {
        for (uint32_t elapsed = 0; elapsed < delay_ms && !fl::platforms::ICoroutineRuntime::instance().isShutdownRequested(); elapsed += 1) {
            uint32_t sleep_time = fl::min(1u, delay_ms - elapsed);
            fl::this_thread::sleep_for(fl::chrono::milliseconds(sleep_time));  // ok sleep for
        }
        p.complete_with_error(error);
    });

    fl::platforms::register_background_thread(fl::move(t));
    return p;
}

FL_TEST_CASE("await in coroutine - basic resolution") {
    fl::atomic<bool> test_completed(false);