PERF: Groupby.shift dont re-call libgroupby.group_shift_indexer
ATM we're calling libgroupby.group_shift_indexer for every column, but we only need to call it once.
wow is there a relevant asv that improves here? > wow is there a relevant asv that improves here?

There are a few that reach here, but they are all single-column so won't see a boost.  #42841 adds multi-column cases to some of those