pub fn traversal_excludes<'b>(&'b self) -> impl Iterator<Item = &'g PackageId> + 'b {
        let excludes = self.make_traversal_excludes();
        excludes.iter()
    }
Returns the packages currently excluded during graph traversals.

Also returns the Hakari package if specified. This is because the Hakari package is treated
as excluded while performing unification.
tools/hakari/src/hakari.rs