ci: Use uv for install on ReadTheDocs (#2475)

* RTD doesn't support uv at the same level as pip, but there are ways
  to still use it along with most of the infrastructure. Adopt the
  strategy provided in ReadTheDocs's 'Build process customization' section
  https://docs.readthedocs.io/en/latest/build-customization.html#install-dependencies-with-uv
  , from readthedocs/readthedocs.org#11152,
  but continue to monitor alternative faster methods such as those
  described in readthedocs/readthedocs.org#11289 .

.readthedocs.yaml

@@ -13,18 +13,17 @@ build:
   apt_packages:
     - curl
     - jq
+  jobs:
+    post_create_environment:
+      - pip install uv
+    post_install:
+      # VIRTUAL_ENV needs to be set manually for now.
+      # See https://github.com/readthedocs/readthedocs.org/pull/11152/
+      - VIRTUAL_ENV=$READTHEDOCS_VIRTUALENV_PATH uv pip install '.[docs]'
 
 # Build documentation in the docs/ directory with Sphinx
 sphinx:
    configuration: docs/conf.py
 
 # If using Sphinx, optionally build your docs in additional formats such as PDF and ePub
 formats: all
-
-# python -m pip install '.[docs]'
-python:
-  install:
-    - method: pip
-      path: .
-      extra_requirements:
-        - docs