Release v2.4.1

• change: ring_check task now terminates the build with an error when any glycan ring is found to be pierced; because glycan residues are covalently bonded to the protein they cannot be deleted, so pestifer logs each offending segment and residue and raises a RuntimeError; the recommended remedy is to rebuild with a different random seed or add more minimization before the ring_check task; non-glycan piercings (e.g. sterol rings) continue to be handled by the delete parameter as before