fix: Restore pyarrow predicate conversion for is_in

[erandagan]

Closes #26802

AI DIsclosure:

1. I used Claude Code while working on this pull request.
2. I confirm that I have reviewed all changes myself, and I believe they are relevant and correct.

[codecov]

Codecov Report

❌ Patch coverage is 69.56522% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.66%. Comparing base (9f1a742) to head (d491925).
⚠️ Report is 46 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-plan/src/plans/python/pyarrow.rs	69.56%	14 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #26811      +/-   ##
==========================================
+ Coverage   81.30%   81.66%   +0.35%     
==========================================
  Files        1802     1805       +3     
  Lines      246972   248038    +1066     
  Branches     3086     3132      +46     
==========================================
+ Hits       200810   202549    +1739     
+ Misses      45371    44683     -688     
- Partials      791      806      +15     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[nameexhaustion]

This doesn't seem right.. we cannot apply the current conversion on AnyValue::List as we would lose a nesting level on list conversion.

Could you re-work this to ensure the conversion happens as an exception only for the RHS of the is_in() operation?

[erandagan]

This doesn't seem right.. we cannot apply the current conversion on AnyValue::List as we would lose a nesting level on list conversion.

Could you re-work this to ensure the conversion happens as an exception only for the RHS of the is_in() operation?

@nameexhaustion Apologies for missing this, I'm not too familiar with the intricacies of the codebase. Pushed a fix.

[nameexhaustion]

Can we make this only do the conversion if we have Literal(List(s)) (i.e. remove the leading predicate_to_pa().or_else. It's otherwise not correct to convert the RHS since the semantics are different