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

include/splash_screen.h

@@ -0,0 +1,13 @@
+#ifndef SPLASH_SCREEN_H
+#define SPLASH_SCREEN_H
+
+#include <tonc.h>
+
+#define SPLASH_FPS 60
+#define SPLASH_DURATION_SECONDS 10
+#define SPLASH_DURATION_FRAMES (SPLASH_FPS * SPLASH_DURATION_SECONDS)
+
+void splash_screen_init();
+void splash_screen_update(uint timer);
+
+#endif // SPLASH_SCREEN_H