Stop compressing full chain when stuck: use on-the fly then instead
Stop compressing full chain when stuck: use on-the fly then instead

Also raise the convergence threshold if catastrophic cancellation is severe


Former-commit-id: 626c1dfc567e47cdaee326d305273828097da68c
DavidAce/DMRG,DavidAce/DMRG,DavidAce/DMRG,DavidAce/DMRG