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/validator.js

@@ -4,7 +4,7 @@ exports = module.exports = {
     isEmail
 };
 
-const assert = require('assert');
+const assert = require('node:assert');
 
 // this currently does not match: "john.doe"@example.com, user@[192.168.1.1], john.doe(comment)@example.com or 用户@例子.世界
 function isEmail(email) {