fix: Add ObjType forward declaration to prevent typedef redefinition errors

Author: ProgrammerKR

include/common.h

@@ -52,6 +52,7 @@ typedef struct Obj Obj;
 typedef struct ObjString ObjString;
 typedef struct ObjFunction ObjFunction;
 typedef struct ObjNative ObjNative;
+typedef enum ObjType ObjType;
 typedef struct Table Table;
 typedef struct Entry Entry;
 typedef struct ValueArray ValueArray;