A modest 15% speedup on docs build times (#9098)

.readthedocs.yaml

@@ -9,6 +9,13 @@ build:
   os: ubuntu-22.04
   tools:
     python: "3.11"
+  commands:
+    - python -mvirtualenv $READTHEDOCS_VIRTUALENV_PATH
+    - python -m pip install --upgrade --no-cache-dir pip setuptools
+    - python -m pip install --upgrade --no-cache-dir sphinx readthedocs-sphinx-ext
+    - python -m pip install --exists-action=w --no-cache-dir -r docs/requirements.txt
+    - cat docs/conf.py
+    - python -m sphinx -T -E -b html -d ./docs/_build/doctrees -D language=en ./docs $READTHEDOCS_OUTPUT/html -j 8
 
 # Build documentation in the "docs/" directory with Sphinx
 sphinx: