A bit of refactor to put apply in Animation where it belongs.

tests/animation.cpp

@@ -42,7 +42,7 @@ TEST_CASE("animation utility API", "[animation]") {
 
   anim.play();
 
-  while(animation::apply(anim, *blanket.sprite, {0,0})) {
+  while(anim.apply(*blanket.sprite, {0,0})) {
     fmt::println("animation: {}", anim.subframe);
   }
 }

tests/animation2.cpp

@@ -32,7 +32,7 @@ struct AnimationState {
   }
 
   void apply(textures::SpriteTexture& st) {
-    animation::apply(anim, *st.sprite, pos);
+    anim.apply(*st.sprite, pos);
   }
 };