feat(python): Expose plan and expression nodes through NodeTraverser to Python

[wence-]

This is a (reasonably complete) exposing of the IR and AExpr enums via #[pyclass] structs to Python.

The best place to start a review is probably visitor/nodes.rs (the expr_nodes.rs wrapping of expressions follows the same pattern, but there are more structs to go through). I am reasonably happy with the structure, but not fully up-to-speed on the most idiosyncratic ways of doing things. For example, should I implement ToPyObject for Wrap<&IR> rather than having an into_py free function?

[codspeed-hq]

CodSpeed Performance Report

Merging #15776 will not alter performance

_{Comparing wence-:wence/fea/nodes (e8bec35) with main (9c96dca)}

Summary

✅ 13 untouched benchmarks

[ritchie46]

Thanks @wence-.

I think going via the free function is fine for now as long as we don't expose it further than the visitor. I've left one comment, other than that looks fine to me. 👍

[codecov]

Codecov Report

Attention: Patch coverage is 5.26811% with 1007 lines in your changes are missing coverage. Please review.

Project coverage is 80.68%. Comparing base (f0dbb6a) to head (7ac6dd5).

❗ Current head 7ac6dd5 differs from pull request most recent head af86abd. Consider uploading reports for the commit af86abd to get more accurate results

Files	Patch %	Lines
py-polars/src/lazyframe/visitor/expr_nodes.rs	0.79%	499 Missing ⚠️
py-polars/src/lazyframe/visitor/nodes.rs	0.00%	363 Missing ⚠️
py-polars/src/lazyframe/visit.rs	0.00%	136 Missing ⚠️
py-polars/src/conversion/mod.rs	0.00%	7 Missing ⚠️
py-polars/src/lib.rs	96.29%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15776      +/-   ##
==========================================
- Coverage   81.29%   80.68%   -0.61%     
==========================================
  Files        1381     1370      -11     
  Lines      176876   176046     -830     
  Branches     3043     2530     -513     
==========================================
- Hits       143789   142045    -1744     
- Misses      32604    33527     +923     
+ Partials      483      474       -9     

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[ritchie46]

Cool, shall we get this in?

[wence-]

Cool, shall we get this in?

Yes, I think this is good to go. Note it's currently targetted at python_visit. I can retarget or you can merge there and then merge that branch in.

[ritchie46]

Oh, yeah, let's target to main directly. 👍