Update furo requirement in the production-dependencies group (#12)

Updates the requirements on [furo](https://github.com/pradyunsg/furo) to permit the latest version.

Updates `furo` to 2025.7.19
- [Release notes](https://github.com/pradyunsg/furo/releases)
- [Changelog](https://github.com/pradyunsg/furo/blob/main/docs/changelog.md)
- [Commits](pradyunsg/furo@2024.08.06...2025.07.19)

---
updated-dependencies:
- dependency-name: furo
  dependency-version: 2025.7.19
  dependency-type: direct:production
  dependency-group: production-dependencies
...

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Author: dependabot[bot]

requirements-docs.txt

@@ -1,5 +1,5 @@
 sphinx~=6.0.0
-furo~=2024.8.6
+furo~=2025.7.19
 sphinx_copybutton~=0.5.1
 sphinx-remove-toctrees~=1.0.0
 nbsphinx~=0.9.3