Iterate an MVCC b-tree cursor selecting the most recent version of a record.
Designate takes a map of valid versions. It will skip records that do not have a version in the valid version map, then select the greatest version from the available versions. It also mainatins a list of versions visisted during the iteration. This is used to implement multi-version concurrency control in a Strata b-tree and is part of the MVCC library and the Strata universe.