More restrictive input validation during predicate pushdown filter extraction

[charlesbluca]

While running some TPC-H queries using dask-sql + dask-cudf, I noticed some failures around predicate pushdown that seemed to be caused by us incorrectly pushing down blockwise comparisons between columns.

This PR attempts to tighten the logic of _blockwise_comparison_dnf to block this edge case; marking this as draft as I'm not sure if we want to block all RHS getitem calls yet.

cc @rjzamora

[codecov-commenter]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (2f068f9) 85.55% compared to head (d841dcc) 85.51%.

Files	Patch %	Lines
dask_sql/physical/utils/filter.py	0.00%	1 Missing and 1 partial ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1269      +/-   ##
==========================================
- Coverage   85.55%   85.51%   -0.05%     
==========================================
  Files          77       77              
  Lines        4257     4259       +2     
  Branches      758      759       +1     
==========================================
  Hits         3642     3642              
- Misses        446      447       +1     
- Partials      169      170       +1     

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