Make stat a method on CloudPath class

[pjbull]

Make stat a method instead of a property to follow pathlib API.

Note: this is technically a potentially breaking change for anyone who implemented their own plugin CloudPath subclass, but didn't override stat. All of our classes override stat as a method properly.

Bonus fix for #203 since upstream breaking change was fixed we can unpin our pytest version

Fixes #234
Fixes #203

[github-actions]

🚀 Deployed on https://deploy-preview-250--gallant-agnesi-5f7bb3.netlify.app

[codecov-commenter]

Codecov Report

Merging #250 (db77d18) into master (4cc0d33) will decrease coverage by 0.1%.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master    #250     +/-   ##
========================================
- Coverage    95.0%   94.8%   -0.2%     
========================================
  Files          21      21             
  Lines        1324    1323      -1     
========================================
- Hits         1258    1255      -3     
- Misses         66      68      +2     

Impacted Files	Coverage Δ
cloudpathlib/cloudpath.py	93.5% <ø> (-0.5%)	⬇️