Add list_unlink() for safe node removal from ready queue

Previously, the list operation for removal was limited to
list_remove(), which immediately freed the list node during the
function call. When removing a running task (TASK_RUNNING), the list
node in the ready queue must not be freed because kcb->task_current
shares the same node.

This change introduces list_unlink(), which detaches the node from
the list without freeing it. The unlinked node is returned to the
caller, allowing safe reuse and improving flexibility in dequeue
operations.

This API will be applied in sched_dequeue_task() for safely removing
tasks from ready queues.

Author: vicLin8712

include/lib/list.h

@@ -134,6 +134,25 @@ static inline void *list_remove(list_t *list, list_node_t *target)
     return data;
 }
 
+/* Unlink a node from list without freeing node */
+static inline void list_unlink(list_t *list, list_node_t *target)
+{
+    if (unlikely(!list || !target || list_is_empty(list)))
+        return;
+
+    list_node_t *prev = list->head;
+    while (prev->next != list->tail && prev->next != target)
+        prev = prev->next;
+
+    if (unlikely(prev->next != target))
+        return; /* node not found */
+
+    prev->next = target->next;
+    target->next = NULL;
+    list->length--;
+    return;
+}
+
 /* Iteration */
 
 /* Callback should return non-NULL to stop early, NULL to continue */