pub fn build_dep_links<'a>(
        &'a self,
    ) -> impl Iterator<Item = PackageLink<'g>> + ExactSizeIterator + 'a {
        let package_graph = self.target_features.graph().package_graph;
        self.build_dep_edge_ixs
            .iter()
            .map(move |edge_ix| package_graph.edge_ix_to_link(*edge_ix))
    }
Returns `PackageLink` instances for build dependencies from target packages.

## Notes

For each link, the `from` is built on the target while the `to` is built on the host.
It is possible (though rare) that a build dependency is also included as a normal
dependency, or as a dev dependency in which case it will also be built on the target.

The returned iterators will not include build dependencies of host packages -- those are
also built on the host.
guppy/src/graph/cargo/cargo_api.rs