test: ds: update to use new object system

ds-test/trees.c

@@ -33,7 +33,7 @@ int main(void)
 	b_dict_foreach(&it, dict)
 	{
 		printf("item %zu: %s=%d\n", it.i, b_string_ptr(it.key),
-		       b_number_get_int(B_NUMBER(it.value)));
+		       b_number_get_int(it.value));
 	}
 
 	b_tree *tree = b_tree_create();
@@ -112,8 +112,8 @@ int main(void)
 		printf("%d\n", item->value);
 	}
 
-	b_tree_release(tree);
-	b_dict_release(dict);
+	b_tree_unref(tree);
+	b_dict_unref(dict);
 
 	return 0;
 }