feat: add support for last_day expression

[andygrove]

Summary

• Adds native Comet support for Spark's last_day function
• Returns the last day of the month for a given date
• Uses the SparkLastDay implementation from the datafusion-spark crate

Test Plan

• Added unit tests with random dates
• Added tests for literal dates across various months
• Added tests for leap year handling (February 2024 vs 2023)
• Added test for null handling
• Verified all existing tests pass

Note: This PR was generated with AI assistance.

Closes #3090

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.04%. Comparing base (f09f8af) to head (399aa84).
⚠️ Report is 861 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #3143      +/-   ##
============================================
+ Coverage     56.12%   60.04%   +3.92%     
- Complexity      976     1429     +453     
============================================
  Files           119      170      +51     
  Lines         11743    15774    +4031     
  Branches       2251     2606     +355     
============================================
+ Hits           6591     9472    +2881     
- Misses         4012     4981     +969     
- Partials       1140     1321     +181     

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[comphead]

Thanks @andygrove