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/shell.js

@@ -1,10 +1,10 @@
 'use strict';
 
-const assert = require('assert'),
+const assert = require('node:assert'),
     BoxError = require('./boxerror.js'),
-    child_process = require('child_process'),
+    child_process = require('node:child_process'),
     debug = require('debug')('box:shell'),
-    path = require('path'),
+    path = require('node:path'),
     safe = require('safetydance'),
     _ = require('./underscore.js');