chore: Add linux support and containerize the project - #5

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, actions/setup-dotnet@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Null should not be used for type parameter 'input' of type 'string'. Use a non-null value, or convert the parameter to a nullable type. (https://xunit.net/xunit.analyzers/rules/xUnit1012)