Bump furo from 2025.9.25 to 2025.12.19 (#2915)

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](https://github.com/pradyunsg/furo/compare/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>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
diff --git a/doc/requirements.txt b/doc/requirements.txt
index cf9e808..a759a74 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -1,3 +1,3 @@
 -e .
 sphinx~=8.1
-furo==2025.9.25
+furo==2025.12.19