fix: add reduce to allow errors to be pickled

[bcvandendool]

Fixes

Fixes #139
When an error occurs when running the library in a celery shared task, celery tries to pickle the error which fails. This is because the init function requires a parameter that it cannot automatically reconstruct from the info stored in the class. This modifies the init function to allow both the original way of initializing, as well as being able to specify all the arguments separately. The reduce function has been implemented to explicitly tell it how it should pickle this class, and which parameters to use. A test has been added to show that the errors can now be pickled.

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the Contribution Guidelines and my PR follows them
• I have titled the PR appropriately
• I have updated my branch with the main branch
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation about the functionality in the appropriate .md file
• I have added inline documentation to the code I modified

If you have questions, please file a support ticket, or create a GitHub Issue in this repository.

[codecov]

Codecov Report

Merging #148 (c75074c) into main (6d62911) will increase coverage by 0.32%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #148      +/-   ##
==========================================
+ Coverage   95.14%   95.46%   +0.32%     
==========================================
  Files           6        6              
  Lines         309      331      +22     
==========================================
+ Hits          294      316      +22     
  Misses         15       15              

Impacted Files	Coverage Δ
python_http_client/exceptions.py	97.82% <100.00%> (+0.39%)	⬆️
tests/test_unit.py	99.33% <100.00%> (+0.07%)	⬆️

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[JenniferMah]

Thanks for your PR @bcvandendool!