feat(rust): Implement predicate pushdown for aliased groupby keys

[jberg5]

Addresses #26589.

Previously, predicate pushdown for group_by queries when the group by key was aliased was unimplemented.

AI use: I used Claude with Opus 4.6 to identify this opportunity, implement the test case, and implement the fix. I have verified its correctness myself; I don't think I could have done a better job with the code if I had written this by hand (low bar - I spend a lot more time with Python than I do with Rust 😄 ).

[codecov]

Codecov Report

❌ Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 81.40%. Comparing base (ceb6366) to head (fc8534a).
⚠️ Report is 14 commits behind head on main.

Files with missing lines	Patch %	Lines
...src/plans/optimizer/predicate_pushdown/group_by.rs	94.44%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #26597      +/-   ##
==========================================
+ Coverage   81.38%   81.40%   +0.02%     
==========================================
  Files        1792     1795       +3     
  Lines      244406   244988     +582     
  Branches     3078     3079       +1     
==========================================
+ Hits       198911   199444     +533     
- Misses      44709    44758      +49     
  Partials      786      786              

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