fix: pushdowns for unpivot

[universalmind303]

closes #3722

[codspeed-hq]

CodSpeed Performance Report

Merging #3724 will improve performances by 16.54%

_{Comparing universalmind303:unpivot-optimizer (3ede568) with main (b31ad6b)}

Summary

⚡ 1 improvements
✅ 26 untouched benchmarks

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	test_iter_rows_first_row[100 Small Files]	231 ms	198.2 ms	+16.54%

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.04%. Comparing base (98a5589) to head (3ede568).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3724      +/-   ##
==========================================
- Coverage   77.91%   77.04%   -0.87%     
==========================================
  Files         727      728       +1     
  Lines       91217    92552    +1335     
==========================================
+ Hits        71068    71311     +243     
- Misses      20149    21241    +1092     

Files with missing lines	Coverage Δ
...lan/src/optimization/rules/push_down_projection.rs	93.61% <100.00%> (+0.71%)	⬆️

... and 10 files with indirect coverage changes