polars.DataFrame.to_arrow() unnecessarily sets string columns as large_string type

[Sara-ShiHo]

Checks

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of Polars.

Reproducible example

df = pl.DataFrame(
    {"foo": [1, 2, 3, 4, 5, 6], "bar": ["a", "b", "c", "d", "e", "f"]}
)
df.to_arrow()

Log output

No response

Issue description

.to_arrow() sets string columns to large_string regardless of data size.

Expected behavior

pandas actually does this correctly.

df = pl.DataFrame(
    {"foo": [1, 2, 3, 4, 5, 6], "bar": ["a", "b", "c", "d", "e", "f"]}
)  # polars
df = df.to_pandas()  # pandas
pa.Table.from_pandas(df)

this results in

pyarrow.Table
foo: int64
bar: string

Installed versions

0.20.19

[Sara-ShiHo]

this is a duplicate #15047