BUG: PeriodIndex + TimedeltaArray-with-NaT
Implements the same round_ok behavior in astype_overflowsafe that we use in Timestamp/Timedelta _as_reso, i.e. this will lead to more code-sharing in follow-ups.
I think the `test_round_sanity` 32 bit failures are unrelated, but is it worth xfailing or fixing soon? > I think the test_round_sanity 32 bit failures are unrelated, but is it worth xfailing or fixing soon?

definitely worth fixing before long

