fix: Remove duplicate ObjType typedef causing CI build errors

- Removed forward declaration 'typedef enum ObjType ObjType;' from common.h
- This was causing typedef redefinition errors in C11 strict mode
- The enum is properly defined in object.h
- Fixes build failures on Ubuntu, Windows, and macOS CI platforms

Author: ProgrammerKR

include/common.h

@@ -52,7 +52,6 @@ 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;