Create a Decorative object class

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

lib/classes/decorative.dart

@@ -0,0 +1,22 @@
+import 'package:wolf_dart/classes/entity.dart';
+
+class Decorative extends Entity {
+  Decorative({
+    required super.x,
+    required super.y,
+    required super.spriteIndex,
+    required super.mapId,
+    super.state = EntityState.staticObj, // Defaults to static
+  });
+
+  // Checks if the Map ID belongs to a standard decoration
+  static bool isDecoration(int objId) {
+    return (objId >= 23 && objId <= 70) || objId == 124;
+  }
+
+  // Safely calculates the VSWAP sprite index for standard decorations
+  static int getSpriteIndex(int objId) {
+    if (objId == 124) return 95; // Dead guard
+    return objId - 21;
+  }
+}