phases: allow registration and boundary advancement with revision sets The core internals either use revision sets already or can trivially use them. Use the new interface in cg1unpacker.apply to avoid materializing the list of all new nodes as it is normally just a revision range. This avoids about 67 Bytes / changeset on AMD64 in peak RSS. Differential Revision: https://phab.mercurial-scm.org/D9232