Add explicit sphinx.configuration key

[lieryan]

This is now required according to "Deprecation of projects using Sphinx or MkDocs without an explicit configuration file"

Ref: https://about.readthedocs.com/blog/2024/12/deprecate-config-files-without-sphinx-or-mkdocs-config/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.98%. Comparing base (55169bb) to head (5709c7f).
⚠️ Report is 18 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #820   +/-   ##
=======================================
  Coverage   94.98%   94.98%           
=======================================
  Files         135      135           
  Lines       26480    26480           
=======================================
  Hits        25152    25152           
  Misses       1328     1328           

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