pub fn explain(
        &self,
        package_id: &'g PackageId,
    ) -> Result<HakariExplain<'g, '_>, guppy::Error> {
        HakariExplain::new(self, package_id)
    }
Returns a `HakariExplain`, which can be used to print out why a specific package is
in the workspace-hack's `Cargo.toml`.

Returns an error if the package ID was not found in the output.
tools/hakari/src/hakari.rs