Replace expect.js with node:assert/strict

expect.js is unmaintained and unnecessary — Node's built-in assert
module covers all our assertion patterns. This also removes expect.js
from package.json dependencies.

Made-with: Cursor

test/package.json

@@ -9,7 +9,6 @@
   "author": "",
   "license": "ISC",
   "devDependencies": {
-    "expect.js": "^0.3.1",
     "mocha": "^11.7.5",
     "selenium-webdriver": "^4.41.0"
   },