Draft: Allow MET to run in the new JO test

Most of the changes in this MR are adding type hints which were helpful in tracking down some errors that I had. The relevant functional changes are in METChainConfiguration and the CVFClusterInputConfig.create_accumulator method in METRecoSequences.py.

There is no guarantee that what is produced here in any way matches the old JO, and in the tracking it is expected not to.