pub fn named(package_id: &'g PackageId, feature_name: &'g str) -> Self {
        Self {
            package_id,
            label: FeatureLabel::Named(feature_name),
        }
    }
Creates a new `FeatureId` representing a named feature in the `[features]` section,
or an implicit named feature created by an optional dependency.
guppy/src/graph/feature/graph_impl.rs