use wpt for testing tree constructor + add support for processing instruction #69 - #68

The strategy configuration was canceled because "build._21" failed

Process completed with exit code 1.

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@v4, actions/checkout@v4, actions/setup-java@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/