frontend: update bluelib api usage

frontend/debug.c

@@ -1,6 +1,6 @@
 #include "debug.h"
 
-#include <blue/object/string.h>
+#include <blue/ds/string.h>
 #include <blue/term.h>
 #include <ivy/asm/lex.h>
 #include <ivy/lang/ast.h>
@@ -212,7 +212,7 @@ extern enum ivy_status print_ast_node(
 	b_string *str = b_string_create();
 	ivy_ast_node_to_string(node, str);
 	b_printf("%s", b_string_ptr(str));
-	b_string_release(str);
+	b_string_unref(str);
 
 #if 0
 	b_puts(ivy_ast_node_type_to_string(node->n_type));