use polars default for time_unit

Author: dfrankland

dataframely/columns/datetime.py

@@ -333,7 +333,7 @@ def __init__(
 
     @property
     def dtype(self) -> pl.DataType:
-        return pl.Datetime(time_unit="us", time_zone=self.time_zone)
+        return pl.Datetime(time_zone=self.time_zone)
 
     def validation_rules(self, expr: pl.Expr) -> dict[str, pl.Expr]:
         result = super().validation_rules(expr)

dataframely/random.py

@@ -334,7 +334,7 @@ def sample_datetime(
             )
             # NOTE: polars tracks datetimes relative to epoch
             - _datetime_to_microseconds(EPOCH_DATETIME)
-        ).cast(pl.Datetime(time_unit="us", time_zone=time_zone))
+        ).cast(pl.Datetime(time_zone=time_zone))
 
         if resolution is not None:
             return result.dt.truncate(resolution)