Add BUILD_RTI guards to InfrastructureManagement and AudioVideoManagement DDS handlers

- ism_dtc_impl_custom.h/cpp: Wrap all DDS-dependent method declarations and implementations with BUILD_RTI guards
- dds_handler.cpp (InfrastructureManagement): Guard RTI DDS initialization code
- dds_handler.h/cpp (AudioVideoManagement): Guard DomainParticipant types and methods
- Enables building without RTI Connext DDS dependencies (BUILD_RTI=OFF)
- Stub types used when guards are disabled

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

qt6-after/qt6-migrated-legatus/Lts/Services/AudioVideoManagement/dds_handler.h

@@ -8,7 +8,9 @@
 #pragma once
 
 #include "logger.h"
+#if BUILD_RTI
 #include <dds/domain/DomainParticipant.hpp>
+#endif
 #include <DDS/Core/topic_lock_master.h>
 #include <QStringList>
 
@@ -73,7 +75,11 @@ public:
    */
   bool enableDtcClients();
 
+#if BUILD_RTI
   dds::domain::DomainParticipant   domainParticipant() const;
+#else
+  void* domainParticipant() const { return nullptr; }
+#endif
 
   std::shared_ptr<Core::Pacemaker>          pacemaker()       const { return m_pacemaker; }
   std::shared_ptr<Core::TopicLockMaster>    topicLockMaster() const { return m_topicLockMaster; }