Add platform-specific requestAnimationFrame, refactor redundant string accessor methods, and introduce BufferedImage and Color classes for emulator graphics rendering.

src/jvmMain/kotlin/mtmc/util/PlatformSpecific.jvm.kt

@@ -1,3 +1,6 @@
 package mtmc.util
 
-actual fun currentTimeMillis(): Long = System.currentTimeMillis()
+actual fun currentTimeMillis(): Long = System.currentTimeMillis()
+actual fun requestAnimationFrame(action: (Double) -> Unit) {
+  error("requestAnimationFrame is not supported on JVM")
+}