Function install 

pub(crate) fn install(
    download_path: &Path,
    install_dir: &Path,
    package_name: &str,
) -> Result<EngineInstallReceipt>

Install an MSIX package and return the receipt data WinBrew needs later.

The function calls into Windows to register the package, creates the target install directory so the install record has a concrete path, and returns an EngineInstallReceipt with EngineKind::Msix plus EngineMetadata::Msix.