Use aliased column names for cross joins

[charlesbluca]

Because we were forgetting to alias/unalias column names before/after the merge operation, tables sharing column names were not being handled properly

[codecov-commenter]

Codecov Report

Merging #1250 (df198d1) into main (3972967) will increase coverage by 0.00%. The diff coverage is 100.00%.

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@@           Coverage Diff           @@
##             main    #1250   +/-   ##
=======================================
  Coverage   85.55%   85.56%           
=======================================
  Files          77       77           
  Lines        4258     4260    +2     
  Branches      758      758           
=======================================
+ Hits         3643     3645    +2     
  Misses        446      446           
  Partials      169      169           

Files	Coverage Δ
dask_sql/physical/rel/logical/cross_join.py	88.88% <100.00%> (+0.88%)	:arrow_up:

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