feat(ci): PR size (non-test churn) pre-commit hook + size-labeling workflow - #445

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