add observer_handler class

src/typedefs.hpp

@@ -4,7 +4,8 @@
 #include <stdint.h>
 
 using scriptenv = std::shared_ptr<int>;
-using observer_handler = std::shared_ptr<int>;
+
+class observer_handler;
 
 /// @brief dynamic integer type (64 bit signed integer)
 using integer_t = int64_t;