[Sync-En] cURL: document multi-handle behavior, update curl-multi-exec purpose, document socket_set_timeout deprecation - #3342

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