test(python): Adjust flaky with_columns test

[nameexhaustion]

I think this fails in CI a bit more often than we'd want - to address this, I've increased num_columns from 2,000 to 10,000. I've also updated the assertion to check the runtime relative to the time taken for applying calling with_columns on 10 columns rather than an exact time.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.37%. Comparing base (402c15e) to head (26c6cf5).
Report is 45 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #19844   +/-   ##
=======================================
  Coverage   79.37%   79.37%           
=======================================
  Files        1550     1550           
  Lines      214743   214743           
  Branches     2460     2460           
=======================================
+ Hits       170457   170461    +4     
+ Misses      43727    43723    -4     
  Partials      559      559           

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