Yet more refactors in basebuffer.

luprex/cpp/core/streambuffer.hpp

@@ -246,7 +246,7 @@ public:
 using LuaValue = BaseLuaValue<eng::string>;
 
 class StreamBufferConfig {
-protected:
+public:
     using string_type = eng::string;
     void *basebuffer_malloc(size_t size) { return eng::malloc(size); }
     void basebuffer_free(void *p) { eng::free(p); }