Working on improving zoneinfo support in pandas, I want to check for non-existent datetimes. e.g.
```
from datetime import datetime, timezone
import zoneinfo
tz = zoneinfo.ZoneInfo("US/Pacific")
dt = datetime(2014, 3, 9, 2, tzinfo=tz) # <- want to tell if this exists
roundtrip = dt.astimezone(timezone.utc).astimezone(tz)
if roundtrip != dt:
raise ValueError("Nonexistent!")
```
Is checking for round-tripping a) correct and b) the suggested way of doing this?
