i.e. when we get pd.Timestamp.now("UTC") we should return a Timestamp with datetime.timezone.utc rather than pytz.UTC. Similarly when we parse an ISO8601 datetime we should use tzinfo of timezone(timedelta(seconds=val*60)) instead of pytz.FixedOffset(val)

This isn't that hard to implement, but doing it breaks a couple dozen tests where we are currently checking for pytz objects. This would technically be an API change, so putting it up for discussion before implementing it.