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/test/reverseproxy-test.js

@@ -9,7 +9,7 @@ const BoxError = require('../boxerror.js'),
     common = require('./common.js'),
     domains = require('../domains.js'),
     expect = require('expect.js'),
-    fs = require('fs'),
+    fs = require('node:fs'),
     paths = require('../paths.js'),
     reverseProxy = require('../reverseproxy.js'),
     safe = require('safetydance');