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/Lts/Services/RoutingServiceNG/main_handler.cpp

@@ -19,6 +19,7 @@
 #include <DDS/Core/pacemaker.h>
 #include <DDS/DTS/generic_dts_impl.h>
 
+#if BUILD_RTI
 namespace RoutingService
 {
 
@@ -102,3 +103,4 @@ void MainHandler::shutdown()
 }
 
 } // namespace RoutingService
+#endif // BUILD_RTI