Add path smoothing

game/pathfinding.h

@@ -13,12 +13,19 @@ typedef struct PathNode {
     TilePosition pos;
 } PathNode;
 
+typedef struct PathClosedNode {
+    bool visited : 1;
+    i8 x : 3;
+    i8 y : 3;
+} PathClosedNode;
+
 typedef struct PathfindingDesc {
     Position start;
     Position target;
     BzObjectPool *pool;
     BzTileMap *map;
-    PathNode *openSet; // heap
+    PathNode *openSet; // heap (size: width * height)
+    PathClosedNode *closedSet; // size: width * height
     Path *outPath;
 } PathfindingDesc;