Use uv to manage docs Python dependencies

It doesn't make much of a difference to performance in CI, as the docs
dependencies install time is dominated by getting Doxygen, but uv's use
of a lockfile does make builds more reliable.

.github/workflows/ci.yml

@@ -176,24 +176,26 @@ jobs:
         run: ctest --test-dir build --build-config ${{ env.CMAKE_CONFIG }} --output-on-failure --parallel
 
       - name: Install packages for building docs (Linux)
-        working-directory: cpp
+        working-directory: cpp/docs
         run: |
           sudo apt-get update
           sudo apt-get install -y --no-upgrade doxygen
-          pip3 install --user -r docs/requirements.txt
+          pipx install uv
+          uv sync
         if: runner.os == 'Linux'
 
       - name: Install packages for building docs (Windows)
-        working-directory: cpp
+        working-directory: cpp/docs
         run: |
           nuget install doxygen -Version 1.8.14
           echo "${{ github.workspace }}\Doxygen.1.8.14\tools" | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append
-          python -m pip install -r docs/requirements.txt
+          pipx install uv
+          uv sync
         if: runner.os == 'Windows'
 
       - name: Build docs
-        working-directory: cpp
-        run: sphinx-build -b html docs build/docs/html
+        working-directory: cpp/docs
+        run: uv run -- sphinx-build -b html . ../build/docs/html
 
       - name: Package the C++ wrapper
         working-directory: cpp/build

.github/workflows/release.yml

@@ -87,15 +87,16 @@ jobs:
           python-version: '3.13'
 
       - name: Install packages for building docs
-        working-directory: cpp
+        working-directory: cpp/docs
         run: |
           nuget install doxygen -Version 1.8.14
           echo "${{ github.workspace }}\Doxygen.1.8.14\tools" | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append
-          python -m pip install -r docs/requirements.txt
+          pipx install uv
+          uv sync
 
       - name: Build docs
         working-directory: cpp
-        run: sphinx-build -b html docs build\docs\html
+        run: uv run -- sphinx-build -b html . ../build/docs/html
 
       - name: Build archive
         id: build-archive