refactor: split up arrow_expression module

[maruschin]

What changes are proposed in this pull request?

Split arrow_expression.rs into a dedicated submodule.
Move tests and utility functions to separate files for better organization and maintainability.
This solves the issue 745.

How was this change tested?

existing UT

[scovich]

NOTE: Github did not detect that the code was moved. So I manually diffed each new file against the original to detect any changes made during code movement, e.g.:

git diff -b maruschin/split_up_arrow_expression~1:kernel/src/engine/arrow_expression.rs maruschin/split_up_arrow_expression:kernel/src/engine/arrow_expression/tests.rs

Everything looks good except a few private functions that should be changed to pub(crate) instead of pub.

[codecov]

Codecov Report

Attention: Patch coverage is 85.17350% with 94 lines in your changes missing coverage. Please review.

Project coverage is 84.38%. Comparing base (34b9d1a) to head (5e8987e).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
kernel/src/engine/arrow_expression/mod.rs	55.00%	36 Missing and 9 partials ⚠️
...src/engine/arrow_expression/evaluate_expression.rs	82.82%	15 Missing and 13 partials ⚠️
kernel/src/engine/arrow_expression/apply_schema.rs	82.64%	13 Missing and 8 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #750      +/-   ##
==========================================
- Coverage   84.39%   84.38%   -0.01%     
==========================================
  Files          77       80       +3     
  Lines       19226    19222       -4     
  Branches    19226    19222       -4     
==========================================
- Hits        16225    16220       -5     
- Misses       2198     2200       +2     
+ Partials      803      802       -1     

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[nicklan]

Awesome thanks! Do change the visibility things scovich flagged, and maybe write a bit more of a description (as that's what will end up in the git history).

Otherwise looks great, thanks.

[maruschin]

Corrected all comments.

[scovich]

LGTM, thanks!

[zachschuermann]

lgtm

[nicklan]

lgtm! Thanks for your contribution