Potential integer overflow in timer tick handling

[HeatCrab]

During the review of PR #59, potential wrap-around issues were identified in kernel/timer.c.

The current implementation uses direct comparison for timer deadlines:

void _timer_tick_handler(void)
{
	// omitted

        if (now >= t->deadline_ticks) {
            expired_timers[expired_count++] = t;
            kcb->timer_list->head->next = node->next;
            kcb->timer_list->length--;
            return_timer_node(node);
	
	// omitted
}

And for Sorting timers:

/* Sorted insert with early termination for common cases */
static int32_t timer_sorted_insert(timer_t *timer)
{
    // omitted
	
    /* Find insertion point */
    while (prev->next != kcb->timer_list->tail) {
        timer_t *current_timer = (timer_t *) prev->next->data;
        if (timer->deadline_ticks < current_timer->deadline_ticks)
            break;
        prev = prev->next;
    }

    // omitted
}

When the system tick counter (mo_ticks()) wraps around:

1. A timer set for a future time (small value after wrap) might be interpreted as expired immediately if compared against a large now value before the wrap.
2. A timer set for a distant future (large value) might be ignored if now has wrapped to a small value.
3. The timer_sorted_insert logic will incorrectly order timers that span across the wrap-around point.