move from materials-per-map to global, hash validated materials folder with per-map fallback - #76

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v3, microsoft/setup-msbuild@v1, NuGet/setup-nuget@v1.0.5. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/