Drop unnecessary dependency on mock

[avalentino]

Mock is only used in docs/conf.py but the unittest.mock from the standard library is used so an external mock dependency is not needed.

TODO:

• Unit tests and/or doctests in docstrings
• Tests pass locally
• Docstrings and API docs for any new/modified user-facing classes and functions
• Changes documented in docs/release.rst
• Docs build locally
• GitHub Actions CI passes
• Test coverage to 100% (Codecov passes)

[jakirkham]

Lovely! Thank you Antonio 🙏

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.88%. Comparing base (ad1ad67) to head (954c833).
Report is 40 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #643   +/-   ##
=======================================
  Coverage   99.88%   99.88%           
=======================================
  Files          62       62           
  Lines        2708     2708           
=======================================
  Hits         2705     2705           
  Misses          3        3