Try to refine pivot in choose_pivot

[tkf]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 76.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 71.97%. Comparing base (5dd6143) to head (15e9ee1).

Files with missing lines	Patch %	Lines
src/quicksort.jl	72.72%	6 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##           copy-twice     #188      +/-   ##
==============================================
+ Coverage       71.50%   71.97%   +0.46%     
==============================================
  Files              11       11              
  Lines             537      553      +16     
==============================================
+ Hits              384      398      +14     
- Misses            153      155       +2     

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