REFACTOR: Pathlib refactor: circuit.py

[anur7]

issue #5180
In this PR Pathlib refactor is done on circuit.py and test_21_Circuit.py
Close #5882

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[codecov]

Codecov Report

Attention: Patch coverage is 97.95918% with 1 line in your changes missing coverage. Please review.

Project coverage is 84.91%. Comparing base (4d786bf) to head (83ef076).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5842      +/-   ##
==========================================
- Coverage   84.92%   84.91%   -0.02%     
==========================================
  Files         161      161              
  Lines       62156    62166      +10     
==========================================
+ Hits        52785    52786       +1     
- Misses       9371     9380       +9     

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[SMoraisAnsys]

Thanks for the contribution @anur7 !

Can you apply the changes I proposed on multiple locations ? I didn't ping every cases as there seemed to be multiples, but the pattern is often the same. For example, converting a variable into Path at the beginning of the method (or early) and then converting it back to str when needed; adding Path as an expected type in the function docstring, ...

Changes implemented