Add a comment on testing rotateRight/rotateLeft

lib/gen/generator.dart

@@ -263,6 +263,8 @@ class Vault {
     return Vault(tiles2, vx, vy, smooth.flip());
   }
 
+  // TODO: Actually test this logic.
+  // It feels right in my head but that doesn't mean it's right
   Vault rotateRight() {
     List<LevelTile> tiles2 = [
       for (var x = 0; x < vx; x++)