fix: apply parse5-utils JSDoc->TS conversion and fix type mismatches

- Convert parse5-utils from JSDoc .js to TypeScript with parse5 v8 API
- Update parse5-utils package.json, tsconfig from fix/node24
- Fix polyfills-loader parse5 type imports for v8 compatibility

Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bennypowers

package-lock.json

@@ -26,8 +26,8 @@
   },
   "scripts": {
     "build": "tsc",
-    "test:node": "TS_NODE_COMPILER_OPTIONS='{\"module\":\"commonjs\",\"moduleResolution\":\"node\"}' mocha \"test/**/*.test.{ts,js,mjs,cjs}\" --require ts-node/register --reporter dot",
-    "test:watch": "TS_NODE_COMPILER_OPTIONS='{\"module\":\"commonjs\",\"moduleResolution\":\"node\"}' mocha \"test/**/*.test.{ts,js,mjs,cjs}\" --require ts-node/register --watch"
+    "test:node": "node --test 'test/**/*.test.mjs'",
+    "test:watch": "npm run test:node -- --watch"
   },
   "files": [
     "dist",