perf: Don't traverse deep datasets that we repr as union in CSE

[ritchie46]

fixes #16067

[codspeed-hq]

CodSpeed Performance Report

Merging #16096 will improve performances by 28.14%

_{Comparing cse (12748a1) with main (6ded6f0)}

Summary

⚡ 1 improvements
✅ 34 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	cse	Change
⚡	test_filter2	2.8 ms	2.2 ms	+28.14%

[codecov]

Codecov Report

Attention: Patch coverage is 82.35294% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 80.97%. Comparing base (d1f3ef4) to head (12748a1).
Report is 1 commits behind head on main.

Files	Patch %	Lines
...lars-plan/src/logical_plan/optimizer/cse/cse_lp.rs	82.35%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16096      +/-   ##
==========================================
- Coverage   80.98%   80.97%   -0.01%     
==========================================
  Files        1386     1386              
  Lines      178465   178479      +14     
  Branches     2877     2877              
==========================================
+ Hits       144523   144532       +9     
- Misses      33450    33454       +4     
- Partials      492      493       +1     

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