CI: Use uv on RTD

.readthedocs.yml

@@ -10,12 +10,23 @@ version: 2
 build:
   os: "ubuntu-22.04"
   tools:
-    python: "3.12"
+    python: "3.13"
   apt_packages:
     - plantuml
 
-  # Bundle assets, because `pip install --editable=.` does not do it.
   jobs:
+
+    # Install dependencies using `uv`.
+    # https://docs.readthedocs.io/en/stable/build-customization.html#install-dependencies-with-uv
+    create_environment:
+       - asdf plugin add uv
+       - asdf install uv latest
+       - asdf global uv latest
+       - uv venv
+    install:
+       - uv pip install -r docs/requirements.txt
+
+    # Bundle assets, because `pip install --editable=.` does not do it.
     pre_build:
       - make bundle-develop
       - cd docs; make bundle-assets
@@ -25,7 +36,3 @@ sphinx:
   builder: html
   configuration: docs/conf.py
   fail_on_warning: true
-
-python:
-  install:
-    - requirements: docs/requirements.txt