[arrow-csv] Schema inference requires csv on disk

[Goffen]

Describe the bug
To be able to infer a schema without storing files to disk I want to be able to call the Format::infer_schema method.

It's there and seems to work, but it's not exposed so cannot be used outside of library.

To Reproduce
Only method exposed regarding schema inference is infer_schema_from_files which is not great to keep things in memory.

Expected behavior
Format to be public, or some other function being public

[Goffen]

My bad, it was exported under reader as arrow_csv::reader::Format