Upgrade to class_group_vdf.0.0.4 and irmin.3.3.2

This MR updates irmin to 3.3.2 and class_group_vdf to 0.0.4, which includes a fix for the VDF library required to compute proofs of higher difficulty, as set in !5848 (merged). The manifest has also been changed to require these versions.

Corresponding opam-repoistory MR: opam-repository!340 (merged)