audio_core: Misc. improvements to stream/buffer/audio_out.

src/audio_core/buffer.h

@@ -4,6 +4,7 @@
 
 #pragma once
 
+#include <memory>
 #include <vector>
 
 #include "common/common_types.h"
@@ -34,4 +35,6 @@ private:
     std::vector<u8> data;
 };
 
+using BufferPtr = std::shared_ptr<Buffer>;
+
 } // namespace AudioCore