Replace os by pathlib and adapt some tests

[aidanjungo]

linked to #12

[codecov]

Codecov Report

Base: 85.52% // Head: 85.50% // Decreases project coverage by -0.02% ⚠️

Coverage data is based on head (0d29496) compared to base (2e6f026).
Patch coverage: 78.57% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #23      +/-   ##
==========================================
- Coverage   85.52%   85.50%   -0.03%     
==========================================
  Files           6        6              
  Lines         670      669       -1     
  Branches      142      143       +1     
==========================================
- Hits          573      572       -1     
  Misses         70       70              
  Partials       27       27              

Impacted Files	Coverage Δ
src/cpacspy/cpacspy.py	93.13% <75.00%> (-0.07%)	⬇️
src/cpacspy/utils.py	100.00% <100.00%> (ø)

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