refactor: init takes pointer to pointer for compatibliity

Its better for me this way, its just this little change at least, next
is fucking going and fixig all damn tests, the fucking wors part

include/arraylist.h

@@ -22,7 +22,7 @@ typedef enum {
     ARRLIST_INVALID_SLICE,
 } ArrayListErr;
 
-ArrayList *arraylist_init(size_t capacity, size_t elem_size);
+ArrayListErr arraylist_init(ArrayList **arr, size_t capacity, size_t elem_size);
 ArrayListErr arraylist_destroy(ArrayList **arr);
 ArrayListErr arraylist_clear(ArrayList *arr);
 ArrayList *arraylist_clone(const ArrayList *arr);