Switch CDBICompat and its tests to OptDeps

Switch CDBICompat and its tests to OptDeps

This work is a direct descendant of ilmari's c8dc7d33, even though it does
not contain almost any of the original code. While the original approach was
a big improvement, this commit is taking advantage of all improvements that
took place in OptDep handling in earlier commits. The result (at the expense
of a much much larger changeset) is a skip time of < 0.5s for the entire cdbi
set

ilmari++ # this revamp would not have taken place without your first nudge