fix case of f(scalar, array) invocation

[davidhewitt]

Originally reported in https://pydanticlogfire.slack.com/archives/C06EDRBSAH3/p1736338644684009

This case was completely unhandled, the ColumnarValue::Array argument to the function would be discarded, treating the path entry as null and therefore just returning null overall.

There may yet be another bug lurking in that thread; I'm still investigating.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 74.79675% with 31 lines in your changes missing coverage. Please review.

Project coverage is 84.22%. Comparing base (4956e2b) to head (25fcffd).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/common.rs	75.40%	26 Missing and 4 partials ⚠️
src/rewrite.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #63      +/-   ##
==========================================
+ Coverage   84.17%   84.22%   +0.04%     
==========================================
  Files          15       15              
  Lines         986     1014      +28     
  Branches      986     1014      +28     
==========================================
+ Hits          830      854      +24     
- Misses        109      111       +2     
- Partials       47       49       +2     

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[davidhewitt]

nightly bug is an ICE in rust-lang/rust#135235, not an issue for merge