TZ and zoneinfo support

What is the correct way to convert datetime (utc) to [arbitrary] timezone? Looks like this lib supports neither `zoneinfo` module nor `astimezone()` method...

[Example](https://docs.python.org/3/library/zoneinfo.html) I would like to run in CircuitPython:
```
from datetime import timezone
LOS_ANGELES = ZoneInfo("America/Los_Angeles")
dt_utc = datetime(2020, 11, 1, 8, tzinfo=timezone.utc)

# Before the PDT -> PST transition
print(dt_utc.astimezone(LOS_ANGELES))

# After the PDT -> PST transition
print((dt_utc + timedelta(hours=1)).astimezone(LOS_ANGELES))
```

No source file or test is named. Start by reviewing this repository's datetime subset and the linked CPython zoneinfo example, then determine the scope needed for timezone conversion and astimezone() support. Done means the supplied CircuitPython example works across the PDT-to-PST transition.

Written by the indexing model from the issue text.