Qt6 Migration: BUILD_RTI guards und CMake fixes

- BUILD_RTI conditional compilation für RTI Connext DDS dependencies
- Namespace fixes in core_dtc.h (Core:: → DDS::Core::)
- CMakeLists.txt: BUILD_RTI option und conditional dependencies
- Handler minelayer: namespace closing mit BUILD_RTI guard
- Build erfolgreich mit BUILD_RTI=OFF validiert

Signed-off-by: Torsten Wierschin <torsten.wierschin@life-maps.com>

qt6-after/qt6-migrated-legatus/tests/test_timelineheaderview.cpp

@@ -11,16 +11,21 @@ class TimelineHeaderViewTest : public ::testing::Test
   protected:
     void SetUp() override
     {
-        int argc = 1;
-        char* argv[] = {const_cast<char*>("test")};
-        qApp = new QApplication(argc, argv);
+        static int argc = 1;
+        static char* argv[] = {const_cast<char*>("test")};
+        if (!qApp)
+        {
+            m_app = std::make_unique<QApplication>(argc, argv);
+        }
     }
 
     void TearDown() override
     {
-        delete qApp;
-        qApp = nullptr;
+        m_app.reset();
     }
+
+  private:
+    std::unique_ptr<QApplication> m_app;
 };
 
 TEST(TimelineHeaderViewTest, ConstructorCreatesValidHeader)