mocks(dds): make async dispatcher detached and avoid join-on-clear to prevent test teardown terminate

Lts/DDS/DdsUnitTestsPlaceholder/mocks/MockDDS.cpp

@@ -58,6 +58,8 @@ static void ensure_async_thread() {
     if (!g_async_running) {
         g_async_running = true;
         g_async_thread = std::thread(async_worker);
+        // detach worker so test binary exit doesn't require join; worker will exit when g_async_running is false
+        g_async_thread.detach();
     }
 }
 
@@ -118,17 +120,12 @@ void clear_all() {
         std::lock_guard<std::mutex> lk(g_mtx);
         g_topics.clear();
     }
-    // shutdown async worker gracefully
+    // clear pending async queue; do not join detached worker
-    {
-        std::lock_guard<std::mutex> lk(g_async_mtx);
-        g_async_running = false;
-    }
-    g_async_cv.notify_all();
-    if (g_async_thread.joinable()) g_async_thread.join();
     {
         std::lock_guard<std::mutex> lk(g_async_mtx);
         g_async_queue.clear();
     }
+    g_async_cv.notify_all();
 }
 
 } // namespace MockDDS