feat(sound): add SEUserData and SI2USERDATA

src/sound/SEUserData.hpp

@@ -0,0 +1,9 @@
+#ifndef SOUND_SE_USER_DATA_HPP
+#define SOUND_SE_USER_DATA_HPP
+
+class SEUserData {
+    public:
+        // TODO
+};
+
+#endif

src/sound/SI2USERDATA.hpp

@@ -0,0 +1,19 @@
+#ifndef SOUND_SI2_USER_DATA_HPP
+#define SOUND_SI2_USER_DATA_HPP
+
+#include "sound/SEUserData.hpp"
+#include <cstdint>
+
+class SOUNDKITDEF;
+
+class SI2USERDATA : public SEUserData {
+    public:
+        // Member variables
+        const char* m_name = nullptr;
+        int32_t m_ID = 0;
+        SOUNDKITDEF* m_def = nullptr;
+        int32_t m_type = 0;
+        // TODO
+};
+
+#endif