PERF: Remove Polars PerformanceWarning

[hoxbro]

Remove this warning:

[codecov]

Codecov Report

Attention: Patch coverage is 62.50000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 88.89%. Comparing base (efeda78) to head (701dbb9).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
hvplot/plotting/core.py	62.50%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1418      +/-   ##
==========================================
+ Coverage   88.73%   88.89%   +0.15%     
==========================================
  Files          51       51              
  Lines        7592     7656      +64     
==========================================
+ Hits         6737     6806      +69     
+ Misses        855      850       -5     

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