Fix documentation build: pin packaging==24.1, install with uv.

Documentation builds on readthedocs have been failing due to
a conflict with the `packaging=24.2` package. We can avoid it by
pinning the package. We also ensure reproducible builds by using
uv to install packages from the lockfile.

.readthedocs.yaml

@@ -7,22 +7,18 @@ build:
   os: ubuntu-22.04
   tools:
     python: "3.11"
-  jobs:
-    post_checkout:
-      - bash docs/scripts/readthedocs_fetch_notebook_outputs.sh
+  commands:
+    # Fetch precomputed notebook outputs (if any)
+    - bash docs/scripts/readthedocs_fetch_notebook_outputs.sh
+    # Install and build using uv
+    - asdf plugin add uv
+    - asdf install uv latest
+    - asdf global uv latest
+    - uv sync --extra docs --frozen
+    - uv pip install readthedocs-sphinx-ext
+    - cd docs && uv run python -m sphinx -T -b html -d docs/_build/doctrees -D language=en . $READTHEDOCS_OUTPUT/html
 
 sphinx:
   builder: html
   configuration: docs/conf.py
   fail_on_warning: false
-
-python:
-  install:
-    # Equivalent to 'pip install .'
-    - method: pip
-      path: .
-    # Equivalent to 'pip install .[docs]'
-    - method: pip
-      path: .
-      extra_requirements:
-        - docs

pyproject.toml

@@ -68,13 +68,15 @@ docs = [
     "ipython",
     "flax>=0.8.2",
     "optax",
+    "setuptools",
     "sphinx>=6.0.0,<7.3.0",
     "sphinx-book-theme>=1.0.1",
     "sphinxcontrib-katex",
     "ipython>=8.8.0",
     "myst-nb>=1.0.0",
     "myst-parser>=3.0.1",
     "matplotlib>=3.5.0",
+    "packaging==24.1",
     "sphinx-collections>=0.0.1",
     "sphinx_contributors",
     "sphinx-hoverxref",