statically link GTest, update to 1.18.0, fetch it with CPM - #705

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, conda-incubator/setup-miniconda@v3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

warning libmamba You are using 'pip' as an additional package manager. Be aware that packages installed with 'pip' are managed independently from 'conda-forge' channel.