Refactor priority-change path and introduce sched_migrate_task()

This commit introduces the sched_migrate_task() helper, which handles
migration of a task to the correct ready queue when its priority changes.
If the task is already in a ready queue, the helper dequeues it from the
old priority level, enqueues it into the new one, and updates all related
bookkeeping.

In addition, if a TASK_RUNNING task changes its priority, it now yields
immediately. This ensures that the scheduler always executes tasks in
strict priority order, preventing a running task from continuing to run
at an outdated priority level.

Author: vicLin8712

kernel/task.c

@@ -857,12 +857,22 @@ int32_t mo_task_priority(uint16_t id, uint16_t priority)
         return ERR_TASK_NOT_FOUND;
     }
 
+    bool is_current = (kcb->task_current->data == task);
+
+    /* Removed task from ready queue */
+    if (task->state == TASK_RUNNING || task->state == TASK_READY)
+        sched_migrate_task(task, priority);
+
     /* Update priority and level */
     task->prio = priority;
     task->prio_level = extract_priority_level(priority);
     task->time_slice = get_priority_timeslice(task->prio_level);
 
     CRITICAL_LEAVE();
+
+    if (is_current)
+        mo_task_yield();
+
     return ERR_OK;
 }