feat: add holidays argument to business_day_count

[MarcoGorelli]

Business polars: part 3 of 5

Is there a better way to pass the list of holidays on from Python to Rust?

[codspeed-hq]

CodSpeed Performance Report

Merging #15580 will improve performances by 22.86%

_{Comparing MarcoGorelli:business-holidays (f24eb36) with main (23791bd)}

Summary

⚡ 1 improvements
✅ 21 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	MarcoGorelli:business-holidays	Change
⚡	test_windows_not_cached	3.5 s	2.9 s	+22.86%

[ritchie46]

This should be copied?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.12%. Comparing base (835d198) to head (59930b2).
Report is 10 commits behind head on main.

❗ Current head 59930b2 differs from pull request most recent head f24eb36. Consider uploading reports for the commit f24eb36 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15580      +/-   ##
==========================================
+ Coverage   81.11%   81.12%   +0.01%     
==========================================
  Files        1367     1367              
  Lines      174934   174981      +47     
  Branches     2530     2531       +1     
==========================================
+ Hits       141890   141946      +56     
+ Misses      32569    32559      -10     
- Partials      475      476       +1     

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[ritchie46]

Left one comment on the unsafe tag. After that it is good to go. :)

[MarcoGorelli]

thanks for your review! 🙏
shipping it then to move forwards with the next one