Move voice memory manager code into brand new SPU MMU

src/Library/internal-include/SPU/spu_mmu.hpp

@@ -0,0 +1,9 @@
+#pragma once
+#include <PSX/jabyengine.hpp>
+
+namespace JabyEngine {
+    namespace SPU_MMU {
+        const uint8_t* allocate(uint8_t voice, size_t size);
+        void           deallocate(uint8_t voice);
+    }
+}