fix TimerQueue shutdown race that left cancelled items in the queue (#1200)

~TimerQueue raised m_finish before cancelAll(), and run() exited its loop
without a last checkWork(). A worker woken by cancel() right before the
shutdown left the loop with items still queued: the assert fired in Debug
(Decorator.DestroyTreeWhileTimerIsPending, ~90% of local runs) and in
Release the pending handlers were never invoked with aborted=true.

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

Author: facontidavide

include/behaviortree_cpp/utils/timer_queue.h

@@ -85,8 +85,11 @@ class TimerQueue
 
   ~TimerQueue()
   {
-    m_finish.store(true);
+    // Cancel before raising m_finish: once the worker sees the flag, every
+    // item is already due, so its final checkWork() drains the whole queue.
     cancelAll();
+    m_finish.store(true);
+    m_checkWork.notify();
     if(m_thread.joinable())
     {
       m_thread.join();
@@ -204,6 +207,10 @@ class TimerQueue
       checkWork();
     }
 
+    // The loop may exit without a last pass (e.g. woken up by cancel() right
+    // before the shutdown), leaving cancelled items in the queue.
+    checkWork();
+
     // If we are shutting down, we should not have any items left,
     // since the shutdown cancels all items
     assert(m_items.size() == 0);