Split docs dependencies into separate group, upgrade Sphinx to 9.1.0

Sphinx 9.x requires Python >=3.12, but arcade supports >=3.10. Move
all doc-building deps into a 'docs' dependency group so test CI can
skip them on Python 3.10/3.11 via 'uv sync --no-group docs'.

Also upgrades sphinx-rtd-theme from 3.0.2 to 3.1.0 (required for
Sphinx 9.x compatibility).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Paul V Craven

.github/workflows/test.yml

@@ -38,7 +38,7 @@ jobs:
           enable-cache: true
 
       - name: Sync UV project
-        run: uv sync
+        run: uv sync --no-group docs
 
       - name: Run tests
         env:

pyproject.toml

@@ -38,20 +38,20 @@ Book = "https://learn.arcade.academy"
 extras = [
     "pymunk~=7.2.0"
 ]
+# Doc building (requires Python >=3.12 due to Sphinx 9.x)
+docs = [
+    "sphinx==9.1.0",
+    "sphinx_rtd_theme==3.1.0",
+    "sphinx-rtd-dark-mode==1.3.0",
+    "sphinx-autobuild==2024.10.3",
+    "sphinx-copybutton==0.5.2",
+    "sphinx-sitemap==2.6.0",
+    "sphinx-togglebutton==0.3.2",
+    "pygments==2.19.1",
+    "docutils==0.21.2",
+]
 # Used for dev work
 dev = [
-    "sphinx==8.1.3",               # April 2024 | Updated 2024-07-15, 7.4+ is broken with sphinx-autobuild
-    "sphinx_rtd_theme==3.0.2",     # Nov 2024
-    "sphinx-rtd-dark-mode==1.3.0",
-    "sphinx-autobuild==2024.10.3", # April 2024 | Due to this, Python 3.10+ is required to serve docs
-    "sphinx-copybutton==0.5.2",    # April 2023
-    "sphinx-sitemap==2.6.0",       # April 2024
-    "sphinx-togglebutton==0.3.2",  # May 2025
-    "pygments==2.19.1",            # 2.18 has breaking changes in lexer
-    "docutils==0.21.2",            # ?
-    # "pyyaml==6.0.1",
-    # "readthedocs-sphinx-search==0.3.2",
-    # "sphinx-autodoc-typehints==2.0.1",
     # --- tools and build
     "pytest",
     "pytest-cov",
@@ -65,7 +65,8 @@ dev = [
     "typer==0.12.5",    # Needed for make.py
     "wheel",
     "bottle",            # Used for web testing playground
-    {include-group = "extras"}
+    {include-group = "extras"},
+    {include-group = "docs"},
 ]
 
 # Testing only