build(deps): bump furo from 2025.9.25 to 2025.12.19

Bumps [furo](https://github.com/pradyunsg/furo) from 2025.9.25 to 2025.12.19.
- [Release notes](https://github.com/pradyunsg/furo/releases)
- [Changelog](https://github.com/pradyunsg/furo/blob/main/docs/changelog.md)
- [Commits](pradyunsg/furo@2025.09.25...2025.12.19)

---
updated-dependencies:
- dependency-name: furo
  dependency-version: 2025.12.19
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

docs/requirements.txt

@@ -1,5 +1,5 @@
 click-extra[sphinx]==7.4.0
-furo==2025.9.25
+furo==2025.12.19
 myst-parser==4.0.1
 rstcheck[sphinx]==6.2.5
 rstfmt==0.0.14