CI: Add Windows matrix leg with platform-conditional testing

[Copilot]

• Create .github/workflows/ci.yml with Linux and Windows matrix
• Configure job matrix with ubuntu-latest and windows-latest
• Add conditional test execution: skip NetMap/AF_XDP tests on Windows
• Add conditional test execution: skip WinTun tests on Linux (implicitly handled)
• Configure NuGet package caching (using setup-dotnet built-in)
• Add trigger for push to master and all PRs
• Add explicit permissions block for security best practices
• Fix YAML indentation and .NET SDK version per review feedback
• Verify locally: all builds and tests pass on Linux
• Complete code review and security scanning

Original prompt

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This section details on the original issue you should resolve

<issue_title>CI: Windows matrix leg</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes CI: Windows matrix leg #96

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[Copilot]

Pull request overview

Adds a GitHub Actions CI workflow to provide cross-platform coverage for Magma’s Linux- and Windows-specific components, ensuring the solution is built and tests are executed appropriately per runner OS.

Changes:

• Introduces an OS matrix (ubuntu-latest, windows-latest) with restore/build/test steps.
• Runs all tests on Linux, while running a curated subset of test projects on Windows to avoid Linux-only test projects.
• Adds a Windows-only build verification step for the WinTun sample and sets minimal workflow permissions.

[Copilot]

actions/setup-dotnet installs 10.0.x, but global.json pins the repo to SDK 10.0.102 (roll-forward only within the same feature band). If setup-dotnet installs a different feature band (e.g., 10.0.3xx), dotnet build/test can fail because the required SDK isn’t present. Use 10.0.102 (or a 10.0.1xx range) to match global.json.

Suggested change

	dotnet-version: '10.0.x'
	dotnet-version: '10.0.102'

[Copilot]

NuGet cache path: ~/.nuget/packages is not reliably portable on Windows runners (the cache action doesn’t consistently expand ~ on Windows). Prefer actions/setup-dotnet's built-in NuGet caching (cache: true) or cache ${{ env.USERPROFILE }}\.nuget\packages / ${{ env.NUGET_PACKAGES }} after setting it explicitly.

[benaadams]

@copilot apply changes based on the comments in this thread

[benaadams]

@copilot try again

[Copilot]

@copilot try again

Applied all review feedback in commit 85cd4f8:

• Fixed YAML indentation (steps properly nested under steps:)
• Changed .NET SDK version to 10.0.102 to match global.json
• Replaced manual NuGet cache with setup-dotnet built-in cache: true
• Removed redundant WinTun sample verification step

[benaadams]

Both CI jobs fail at the Setup .NET step with:

Dependencies lock file is not found in /home/runner/work/Magma/Magma. Supported file patterns: packages.lock.json

The actions/setup-dotnet@v4 with cache: true requires a packages.lock.json file to exist in the repo for NuGet package caching. Since this project doesn't use NuGet lock files, the step fails before build/test even run.

Fix: Remove cache: true from the setup-dotnet step:

      - name: Setup .NET
        uses: actions/setup-dotnet@v4
        with:
          dotnet-version: '10.0.102'

Alternatively, if NuGet caching is desired, you'd need to either:

1. Add <RestorePackagesWithLockFile>true</RestorePackagesWithLockFile> to Directory.Build.props and commit the generated packages.lock.json files, or
2. Switch to actions/cache@v4 with a custom key based on **/*.csproj files instead.