Arr.get casts date and datetime columns to integers

[lucazanna]

Polars version checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of Polars.

Issue description

Arr.get does not seem to keep the data type of the column.

Below an example

Reproducible example

import polars as pl
from datetime import datetime

df = pl.DataFrame({
    'date_col': [[datetime(2023,2,1).date(), datetime(2023,2,2).date()]],
    'datetime_col': [[datetime(2023,2,1), datetime(2023,2,2)]]
})

shape: (1, 2)
┌──────────────────────────┬─────────────────────────────────────┐
│ date_col                 ┆ datetime_col                        │
│ ---                      ┆ ---                                 │
│ list[date]               ┆ list[datetime[μs]]                  │
╞══════════════════════════╪═════════════════════════════════════╡
│ [2023-02-01, 2023-02-02] ┆ [2023-02-01 00:00:00, 2023-02-02... │
└──────────────────────────┴─────────────────────────────────────┘

df.with_columns(
    pl.all().arr.get(1).suffix('_element_1')
)

shape: (1, 4)
┌──────────────┬─────────────────────────────────────┬────────────────────┬────────────────────────┐
│ date_col     ┆ datetime_col                        ┆ date_col_element_1 ┆ datetime_col_element_1 │
│ ---          ┆ ---                                 ┆ ---                ┆ ---                    │
│ list[date]   ┆ list[datetime[μs]]                  ┆ i32                ┆ i64                    │
╞══════════════╪═════════════════════════════════════╪════════════════════╪════════════════════════╡
│ [2023-02-01, ┆ [2023-02-01 00:00:00, 2023-02-02... ┆ 19390              ┆ 1675296000000000       │
│ 2023-02-02]  ┆                                     ┆                    ┆                        │
└──────────────┴─────────────────────────────────────┴────────────────────┴────────────────────────┘

Expected behavior

I can cast back the columns to date and datetime, but I would expect arr.get to not change the data type.

Your thoughts?

Installed versions

---Version info---
Polars: 0.16.7
Index type: UInt32
Platform: Linux-5.15.90.1-microsoft-standard-WSL2-x86_64-with-glibc2.31
Python: 3.11.1 (main, Dec  7 2022, 01:11:44) [GCC 9.4.0]
---Optional dependencies---
pyarrow: 11.0.0
pandas: 1.5.2
numpy: 1.24.0
fsspec: <not installed>
connectorx: <not installed>
xlsx2csv: 0.8.1
deltalake: <not installed>
matplotlib: 3.6.2