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_lts_timeline_item_delegate.cpp

@@ -1,4 +1,4 @@
-#include "qt6-after/qt6-migrated-legatus/Lts/Common/LtsTimeline/item_delegate.h"
+#include "Lts/Common/LtsTimeline/item_delegate.h"
 
 #include <gtest/gtest.h>