implement laser target offset

src/ui/GameWorldView.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <optional>
+#include <random>
 #include <set>
 #include <vector>
 
@@ -116,6 +117,7 @@ private:
     {
         FireEvent event;
         qint64    emittedWallMs;
+        QVector2D targetOffset;
     };
 
     struct ToastEntry
@@ -136,6 +138,7 @@ private:
     TickDriver    m_tickDriver;
     QElapsedTimer m_frameTimer;
     qint64        m_wallMs;
+    std::mt19937  m_rng;
     double        m_gameSpeedMultiplier;
     double        m_prevNonZeroSpeed;
     float         m_scrollXTiles;