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/syncer-test.js

@@ -6,11 +6,11 @@
 
 const createTree = require('./common.js').createTree,
     DataLayout = require('../datalayout.js'),
-    execSync = require('child_process').execSync,
+    execSync = require('node:child_process').execSync,
     expect = require('expect.js'),
-    fs = require('fs'),
-    os = require('os'),
-    path = require('path'),
+    fs = require('node:fs'),
+    os = require('node:os'),
+    path = require('node:path'),
     paths = require('../paths.js'),
     safe = require('safetydance'),
     syncer = require('../syncer.js');