Add splash screen functionality and update game state management

- Introduced GAME_SPLASH_SCREEN state in game.h
- Implemented splash_screen_init and splash_screen_update functions in splash_screen.c
- Updated game.c to initialize with GAME_SPLASH_SCREEN and handle splash screen updates
- Removed old splash screen code from main.c

source/affine_background.c

@@ -11,7 +11,6 @@ enum AffineBackgroundID background = AFFINE_BG_MAIN_MENU;
 
 void affine_background_init()
 {   
-    affine_background_change_background(background);
     affine_background_update();
 
     bgaff = bg_aff_default;