feat: Add field expression as selector with an struct scope

[ritchie46]

No description provided.

[ritchie46]

closes #16395

[codspeed-hq]

CodSpeed Performance Report

Merging #16402 will improve performances by 16.1%

_{Comparing field (2616f98) with main (8bc1019)}

Summary

⚡ 1 improvements
✅ 36 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	field	Change
⚡	test_groupby_h2oai_q3	11.5 ms	9.9 ms	+16.1%

[codecov]

Codecov Report

Attention: Patch coverage is 93.84615% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 81.43%. Comparing base (8bc1019) to head (2616f98).

Files	Patch %	Lines
crates/polars-plan/src/dsl/expr.rs	0.00%	1 Missing ⚠️
...plan/src/logical_plan/conversion/expr_expansion.rs	94.11%	1 Missing ⚠️
crates/polars-plan/src/logical_plan/format.rs	0.00%	1 Missing ⚠️
py-polars/polars/functions/lazy.py	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16402      +/-   ##
==========================================
+ Coverage   81.40%   81.43%   +0.03%     
==========================================
  Files        1409     1409              
  Lines      184519   184567      +48     
  Branches     2961     2962       +1     
==========================================
+ Hits       150206   150306     +100     
+ Misses      33798    33745      -53     
- Partials      515      516       +1     

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