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/df.js

@@ -6,7 +6,7 @@ exports = module.exports = {
     prettyBytes
 };
 
-const assert = require('assert'),
+const assert = require('node:assert'),
     BoxError = require('./boxerror.js'),
     debug = require('debug')('box:df'),
     safe = require('safetydance'),