use node: prefix for requires

mostly because code is being autogenerated by all the AI stuff using
this prefix. it's also used in the stack trace.

src/boxerror.js

@@ -2,9 +2,9 @@
 
 'use strict';
 
-const assert = require('assert'),
+const assert = require('node:assert'),
     HttpError = require('@cloudron/connect-lastmile').HttpError,
-    util = require('util');
+    util = require('node:util');
 
 exports = module.exports = BoxError;