build(deps): bump sphinx from 8.2.3 to 9.1.0

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 8.2.3 to 9.1.0.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v8.2.3...v9.1.0)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-version: 9.1.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

docs/requirements.txt

@@ -3,5 +3,5 @@ furo==2025.12.19
 myst-parser==5.0.0
 rstcheck[sphinx]==6.2.5
 rstfmt==0.0.14
-Sphinx==8.2.3
+Sphinx==9.1.0
 sphinx-copybutton==0.5.2