SIGNAL/SLOT migration: socket_handler (5), targettimer (1), socketreader (2) + status update

- Migrated old SIGNAL/SLOT connect syntax to function-pointer syntax
- socket_handler.cpp: timeout, connected, disconnected, readyRead, bytesWritten
- targettimer.cpp: timeout → MyTimerSlot
- socketreader.cpp: readyRead, error (with QOverload for overloaded signal)
- Updated MIGRATION_STATUS.md with migration progress
- Part of Qt5→Qt6 migration with C++17 constraint (RTI 7.7.0 compatibility)

qt6-after/qt6-migrated-legatus/Lts/Services/CentralEffectSimulation/Plugins/TargetAreas/targettimer.cpp

@@ -20,8 +20,8 @@ TargetTimer::TargetTimer(int participantId,
   m_preWarningInterval = preWarningInterval;
   m_timeToEffectInterval = timeToEffectInterval;
   timer = new QTimer(this);
-  connect(timer, SIGNAL(timeout()),
-          this, SLOT(MyTimerSlot()));
+  connect(timer, &QTimer::timeout,
+          this, &TargetTimer::MyTimerSlot);
 
   // msec
 }