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/sftp.js

@@ -7,7 +7,7 @@ exports = module.exports = {
 };
 
 const apps = require('./apps.js'),
-    assert = require('assert'),
+    assert = require('node:assert'),
     blobs = require('./blobs.js'),
     BoxError = require('./boxerror.js'),
     debug = require('debug')('box:sftp'),
@@ -15,7 +15,7 @@ const apps = require('./apps.js'),
     hat = require('./hat.js'),
     infra = require('./infra_version.js'),
     mounts = require('./mounts.js'),
-    path = require('path'),
+    path = require('node:path'),
     paths = require('./paths.js'),
     safe = require('safetydance'),
     services = require('./services.js'),