.NET CI on GitHub Actions

NuGet restore is network-bound and the build is single-threaded.

Why it happens

Restore hits nuget.org for every package, and MSBuild does not parallelise projects unless told to.

What to change

1. Cache ~/.nuget/packages keyed on the lockfile and restore with --locked-mode
2. Build with -m to enable parallel project builds
3. Exclude the workspace from Defender scanning on Windows runners
4. Run tests with --parallel and a matrix over test projects

.NET on runnerhut

jobs:
  build:
    runs-on: runnerhut-8vcpu-windows-2022
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-dotnet@v4
        with: { dotnet-version: '9.0' }
      - run: dotnet restore --locked-mode
      - run: dotnet build -c Release --no-restore -m

The only runnerhut-specific line is `runs-on: runnerhut-8vcpu-windows-2022`. Everything else is standard GitHub Actions — the same actions, the same secrets and the same permissions model you use today.