feat: add timezone handling for datetime in pydantic

[changhiskhan]

If you add timezone information in the Field annotation for a datetime then that will now be passed to the pyarrow data type.

I'm not sure how pyarrow enforces timezones, right now, it silently coerces to the timezone given in the column regardless of whether the input had the matching timezone or not. This is probably not the right behavior. Though we could just make it so the user has to make the pydantic model do the validation instead of doing that at the pyarrow conversion layer.

[eddyxu]

do we want to check whether tz is appropriately serialized

[changhiskhan]

If you put in an invalid timezone pytz will complain. If you put in a tz that doesn't match the schema, then the current behavior is that it'll just get coerced into the timezone that matches the schema.
I was thinking we should ask the user to explicitly add validation to the pydantic model, rather than spreading the validation logic across a bunch of different places. That isn't ideal because if you're not careful you can certainly end up with bad data. But putting this adhoc validator in LanceDB also doesn't feel right 🤷‍♂️

[rok]

I'm not sure how pyarrow enforces timezones,

pyarrow only touches timezones when needed e.g. even cast and subtract won't need it, but floor_temporal will:

import pyarrow as pa
from pyarrow import compute as pc
arr = pa.array([1], pa.timestamp("us", "UTC"))
pc.floor_temporal(arr, unit="week")
arr = arr.cast(pa.timestamp("ns", "XYZ"))
pc.floor_temporal(arr, unit="week")
---
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/rok/venv1/lib/python3.10/site-packages/pyarrow/compute.py", line 262, in wrapper
    return func.call(args, options, memory_pool)
  File "pyarrow/_compute.pyx", line 367, in pyarrow._compute.Function.call
  File "pyarrow/error.pxi", line 144, in pyarrow.lib.pyarrow_internal_check_status
  File "pyarrow/error.pxi", line 100, in pyarrow.lib.check_status
pyarrow.lib.ArrowInvalid: Cannot locate timezone 'XYZ': XYZ not found in timezone database