Add single-soldier coin training addon - #1928

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: MarkusJx/install-boost@8ba8b2fac59ef3d91a838bb4aa53ceabd33d1aa3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/