Add python-arch support (#1079)

Windows ARM64 jobs may need x64 Python independently of their Python
version pin. Add `python-arch` to export `UV_PYTHON_ARCH` for subsequent
steps and include the selected architecture in the uv and managed-Python
cache keys. The input takes precedence over an inherited environment
value, and unsupported uv versions fail before environment creation.

Requires a uv release with `UV_PYTHON_ARCH` support.

action-types.yml

@@ -7,6 +7,8 @@ inputs:
     type: string
   python-version:
     type: string
+  python-arch:
+    type: string
   activate-environment:
     type: boolean
   venv-path: