Make Polars Categorical/Enum to R factor conversion via Rust

[eitsupi]

Currently the conversion to the factor type is performed by calling the factor() function in R.

r-polars/src/rust/src/conversion_s_to_r.rs

Lines 113 to 118 in 6eac27a

	Enum(_, _) => s
	.categorical()
	.map(|ca| extendr_api::call!("factor", ca.iter_str().collect_robj()).unwrap()),
	Categorical(_, _) => s
	.categorical()
	.map(|ca| extendr_api::call!("factor", ca.iter_str().collect_robj()).unwrap()),

but I think it would be possible to perform the conversion on Rust by porting the process from the arrow package.
https://github.com/apache/arrow/blob/26724ab787d12854f109d01571638b099f2bc8a5/r/src/array_to_vector.cpp#L563-L717

[andyquinterom]

Is there any progress on this? I might be able to take the responsability

[eitsupi]

Thanks. Probably no one is working on this at this time.

BTW, we are shifting our focus to the next branch (under development in https://github.com/eitsupi/neo-r-polars) on adding new features, so it might be better to have them work on that.
(Currently the main branch is stuck on updating Rust Polars #1271)