Add compute_dwelltimes_using_poly to sarkit.cphd - #159

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