Regression: Polars 1.14 doesn't accept AWS_S3_ALLOW_UNSAFE_RENAME anymore

[tzugen]

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

storage_options = {
"aws_region": self.region,
"aws_access_key_id": self.access_key,
"aws_secret_access_key": self.secret_key,
"aws_endpoint_url": self.base_url,
"AWS_S3_ALLOW_UNSAFE_RENAME": "true",
}

data_frame.write_delta(
    S3_PATH,
    storage_options=storage_options,
)

Log output

polars.exceptions.ComputeError: unknown configuration key: AWS_S3_ALLOW_UNSAFE_RENAME

same with lowercase:

polars.exceptions.ComputeError: unknown configuration key: aws_s3_allow_unsafe_rename

Issue description

For writing to an S3 without a locking provider AWS_S3_ALLOW_UNSAFE_RENAME needs to be set to true.

This used to work in polars 0.2x

With 1.x the aws props were lowercased and suddenly this variable is not recognized anymore.

Expected behavior

should work

Installed versions

--------Version info---------
Polars:              1.14.0
Index type:          UInt32
Platform:            Linux-6.....
Python:              3.12.7.....
LTS CPU:             False

----Optional dependencies----
adbc_driver_manager  <not installed>
altair               <not installed>
boto3                1.35.64
cloudpickle          <not installed>
connectorx           <not installed>
deltalake            0.21.0
fastexcel            <not installed>
fsspec               2024.10.0
gevent               <not installed>
google.auth          <not installed>
great_tables         <not installed>
matplotlib           <not installed>
nest_asyncio         <not installed>
numpy                2.1.3
openpyxl             3.1.5
pandas               2.2.3
pyarrow              18.0.0
pydantic             2.9.2
pyiceberg            <not installed>
sqlalchemy           2.0.36
torch                <not installed>
xlsx2csv             <not installed>
xlsxwriter           <not installed>

[ion-elgreco]

This pr, addresses it: #19852

[TinoSM]

to me it works, but I recall having issues during scans with that variable set, In 1.14.0 its only allowed for writes

I do use
delta_write_options["engine"] = "rust"