add event system and use it to propagate to print traces

src/lib/sim/Simulation.h

@@ -10,15 +10,16 @@
 
 #include "BeltSystem.h"
 #include "EntityAdmin.h"
-
 #include "entt/entity/entity.hpp"
 #include "SchematicDropEvent.h"
 #include "BuildingType.h"
 #include "BuildingId.h"
+#include "EventHandler.h"
 #include "FireEvent.h"
 #include "GameConfig.h"
 #include "Rotation.h"
 #include "Tick.h"
+#include "TracePrintRequestedEvent.h"
 
 class AiSystem;
 class BuildingSystem;
@@ -29,7 +30,7 @@ class ShipSystem;
 class ScrapSystem;
 class WaveSystem;
 
-class Simulation
+class Simulation: public CombinedEventHandler<TracePrintRequestedEvent>
 {
 public:
     explicit Simulation(GameConfig config, unsigned int seed = 0);
@@ -83,6 +84,8 @@ public:
     const EntityAdmin&    admin() const;
 
 private:
+	void handleEvent(std::shared_ptr<const TracePrintRequestedEvent> event) override;
+
     BuildingId allocateBuildingId();  // Strictly increasing; never returns kInvalidBuildingId.
 
     // Populate HQ, player defence stations, and the first enemy station set.