Implement selectors

[eitsupi]

https://pola-rs.github.io/polars/py-polars/html/reference/selectors.html

[etiennebacher]

They will probably be implemented in Rust at some point, we could wait for that: pola-rs/polars#10594

[etiennebacher]

Also, wait for this to be settled: pola-rs/polars#13757

[eitsupi]

There was a question on Discord regarding column selection.

I think it would be beneficial to users if selectors are available, as I think the current way of column selection using the col function is confusing.

As discussed in the linked issue, the current implementation of Python Polars is problematic, but at least it is the current implementation in version 1.0.0, so it will have been remain to v3.0.0 (2025 summer?).

I have started the initial implementation in https://github.com/eitsupi/neo-r-polars/blob/a5b4525dc60899ade2fe27983381c5ce7b23313f/R/selectors.R.