fix: demolish did not return blocks

src/lib/sim/Simulation.h

@@ -55,6 +55,9 @@ public:
     // Returns the new entity id, or kInvalidEntityId if blocks are insufficient.
     EntityId tryPlaceBuilding(BuildingType type, QPoint anchor, Rotation rotation);
 
+    // Demolishes the building with the given id and refunds building blocks.
+    void demolish(EntityId id);
+
     BuildingSystem&       buildings();
     const BuildingSystem& buildings() const;
     BeltSystem&           belts();