Add a PR, CI workflow that performs a basic install of NuGet packages

[mschofie]

Fixes #20.

Adds an end-to-end scenario test for :/CMakeLists.txt and a GitHub Actions workflow that runs it on Windows, Linux, and macOS.

What's included

• Some pre-cursor fixes:

  • Accommodate 'NuNuGet'/'NuNuGet.exe' naming across platforms
  • ensure_nunuget should make NuNuGet executable on non-WIN32 platforms - Since the NuGet is unpacked as a .zip file, the NuNuGet executable isn't marked as executable. Using file(CHMOD to mark it
  • NUGET_LOCATION should use the lower-case PACKAGE_NAME - The NuGet packages in the global packages folder have a lower-case folder name. Since Linux and MacOS respect the casing, ensure_nunuget needs to be more strict here.

• :/scenarios/basic/ - a self-contained CMake project that exercises :/CMakeLists.txt end-to-end with three packages (Microsoft.Windows.ImplementationLibrary with a floating version, Microsoft.Windows.CppWinRT, Microsoft.Windows.SDK.CPP). After configuration it asserts:

  • NuNuGet was downloaded and the executable exists
  • NUGET_VERSION-* and NUGET_LOCATION-* global properties are set, and the package paths exist on disk
  • Microsoft.Windows.ImplementationLibrary's floating version 1.* resolved to a 1.x release
  • The policy-appropriate find_package hint variable is set (*_ROOT or *_DIR)
  • find_package(Microsoft.Windows.ImplementationLibrary) creates the expected target with valid include directories

• scenarios/basic/Basic.Tests.ps1 - Pester tests that encapsulate the two-step configure logic:

  • Step 1: deletes any existing lock file, runs cmake configure, asserts exit 0 and that packages.lock.json was created
  • Step 2: runs cmake configure again with the existing lock file, asserts exit 0 (verifies lock file consistency)

• .github/workflows/scenario-tests.yml - runs the Pester tests on windows-latest, ubuntu-latest, and macos-latest on every push to main and on pull requests. Uses fail-fast: false so all three platforms always run to completion.

• .gitignore — ignores __* build/tool artifact directories.