perf: Optimize TexturePackerSprite when sprites do not need to be r…

…otated (#3236)

TexturePackerSprite creates unnecessary Transform2D and
Transform2DDecorator objects when region rotation is set to false. This
bloats the TexturePackerSprite object size and causes severe performance
issues when using thousands of TexturePackerSprites. This PR wraps the
creation of these objects in a region rotation check.

---------

Co-authored-by: Lukas Klingsbo <lukas.klingsbo@gmail.com>

packages/flame_texturepacker/lib/src/texture_packer_sprite.dart

@@ -31,9 +31,9 @@ class TexturePackerSprite extends Sprite {
             useOriginalSize ? region.originalHeight : region.height,
           ),
         ) {
-    _decorator = Transform2DDecorator(_transform);
     if (region.rotate) {
-      _transform.angle = math.pi / 2;
+      final transform = Transform2D()..angle = math.pi / 2;
+      _decorator = Transform2DDecorator(transform);
     }
   }
 
@@ -132,8 +132,7 @@ class TexturePackerSprite extends Sprite {
     src = (position ?? Vector2.zero()).toPositionedRect(_srcSize);
   }
 
-  late final Decorator _decorator;
-  final Transform2D _transform = Transform2D();
+  Decorator? _decorator;
 
   // Used to avoid the creation of new Vector2 objects in render.
   static final _tmpRenderPosition = Vector2.zero();
@@ -206,7 +205,7 @@ class TexturePackerSprite extends Sprite {
       -_tmpRenderOffset.x - _tmpRenderImageSize.x,
     );
 
-    _decorator.applyChain(
+    _decorator?.applyChain(
       (applyCanvas) => super.render(
         applyCanvas,
         position: _tmpRenderPosition,