feat: add custom background rendering and speed scaling features for snake gameplay

include/game_render.h

@@ -15,9 +15,12 @@ struct HudCache {
     bool dirty = true;
 };
 
+struct BackgroundContext;
+
 struct RenderAssets {
     PrintConsole *topScreen = nullptr;
     PrintConsole *bottomScreen = nullptr;
+    BackgroundContext *bg_context = nullptr;
 
     u16 *gfx_segment = nullptr;
     u16 *gfx_segment_small = nullptr;