timedWait

pub fn timedWait(sem: *Semaphore, timeout_ns: u64) error{Timeout}!void {
    var timeout_timer = std.time.Timer.start() catch unreachable;

    sem.mutex.lock();
    defer sem.mutex.unlock();

    while (sem.permits == 0) {
        const elapsed = timeout_timer.read();
        if (elapsed > timeout_ns)
            return error.Timeout;

        const local_timeout_ns = timeout_ns - elapsed;
        try sem.cond.timedWait(&sem.mutex, local_timeout_ns);
    }

    sem.permits -= 1;
    if (sem.permits > 0)
        sem.cond.signal();
}