fix: RTD config rename, upgrade OS/Python, add uv setup

- Rename readthedocs.yml to .readthedocs.yml,
- update to Ubuntu 22.04 and Python 3.12,
- add uv setup and mkdocs build commands.

.readthedocs.yaml

@@ -7,12 +7,12 @@ mkdocs:
   configuration: mkdocs.yml
 
 build:
-  os: ubuntu-20.04
+  os: ubuntu-22.04
   tools:
-    python: "3.10"
-
-python:
-  install:
-    - requirements: requirements_dev.txt
-    - method: setuptools
-      path: .
+    python: "3.12"
+  commands:
+    - asdf plugin add uv
+    - asdf install uv latest
+    - asdf global uv latest
+    - uv sync --group docs --frozen
+    - uv run mkdocs build --site-dir $READTHEDOCS_OUTPUT/html