Function install_mrpack 

pub async fn install_mrpack(
    pack_path: &Path,
    instance_name: &str,
    base_dir: &Path,
    java_path: Option<&Path>,
    progress: ProgressFn,
) -> Result<ModpackInstallResult>

Install a .mrpack into instance/{instance_name}.

Files whose client support is required or optional are installed; unsupported ones are skipped. client-overrides/ is applied after overrides/.