allow passing a custom ArqRedis class to create_pool

[jvllmr]

I would like to extend the functionality of the ArqRedis in one of my projects, but I also want to use the original create_pool function. It would be great if the create_pool function would accept a custom class which extends ArqRedis

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 40.00000% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
arq/connections.py	40.00%	3 Missing ⚠️

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@@            Coverage Diff             @@
##             main     #495      +/-   ##
==========================================
- Coverage   96.27%   96.10%   -0.17%     
==========================================
  Files          11       11              
  Lines        1074     1079       +5     
  Branches      209      190      -19     
==========================================
+ Hits         1034     1037       +3     
- Misses         19       21       +2     
  Partials       21       21              

Files with missing lines	Coverage Δ
arq/connections.py	87.50% <40.00%> (-2.57%)	⬇️

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