feat: rewrite $head, $limit, and $tail to be equivalent to Python Polars

[eitsupi]

I noticed that in Python, polars.LazyFrame.head calls the slice method internally.
https://github.com/pola-rs/polars/blob/740e740d9ce3678ea061d5cb4c2bc94892838383/py-polars/polars/lazyframe/frame.py#L4676-L4723

Here these functions are rewritten to match those in Python.
As a result, <DataFrame>$head() and <DataFrame>$tail() now support negative values.

[etiennebacher]

Thanks, LGTM, just a couple of typos.

I wonder why they keep both limit() and head() in the upstream polars if they are identical

[eitsupi]

Thanks for your review.

I wonder why they keep both limit() and head() in the upstream polars if they are identical

It is also strange that LazyFrame in Rust seems to have limit and tail but not head.

Perhaps the reason Python has limit as well as head is to match Rust.