pub fn is_traversal_excluded(&self, package_id: &PackageId) -> Result<bool, guppy::Error> {
        self.graph.metadata(package_id)?;

        let excludes = self.make_traversal_excludes();
        Ok(excludes.is_excluded(package_id))
    }
Returns true if a package ID is currently excluded during traversal.

Also returns true for the Hakari package if specified. This is because the Hakari package is
treated as excluded by the algorithm.

Returns an error if this package ID isn't known to the underlying graph.
tools/hakari/src/hakari.rs