Convert to fileformats/rules to pytest

[pp-mo]

Also moved "test_rules.py" from /fileformats into /fileformats/rules.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.75%. Comparing base (58bb4b1) to head (73926d2).
Report is 9 commits behind head on FEATURE_pytest_conversion.

Additional details and impacted files

@@                    Coverage Diff                     @@
##           FEATURE_pytest_conversion    #5872   +/-   ##
==========================================================
  Coverage                      89.75%   89.75%           
==========================================================
  Files                             92       92           
  Lines                          22940    22940           
  Branches                        5462     5462           
==========================================================
  Hits                           20590    20590           
  Misses                          1619     1619           
  Partials                         731      731           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.