PTHMINT-86: Fix ruff D101

[zulquer]

This pull request introduces minor improvements to the test codebase by adding docstrings to the MockItem classes and makes a small configuration change to the pyproject.toml file.

Test code documentation improvements:

• Added a docstring to the MockItem class in tests/multisafepay/integration/api/base/listings/test_integration_listing_pager.py to clarify its purpose for testing.
• Added a docstring to the MockItem class in tests/multisafepay/unit/api/base/listings/test_unit_listing.py to clarify its purpose for testing.
• Added a docstring to the MockItem class in tests/multisafepay/unit/api/base/listings/test_unit_listing_pager.py to clarify its purpose for testing.

Configuration update:

• Removed "D101" from the ignore list in the extend-safe-fixes section of pyproject.toml, which may affect docstring-related linting for classes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.23%. Comparing base (1db842a) to head (231d931).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #36   +/-   ##
=======================================
  Coverage   90.23%   90.23%           
=======================================
  Files         107      107           
  Lines        2355     2355           
=======================================
  Hits         2125     2125           
  Misses        230      230           

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