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.

__tests__/helpers/setup-inputs.ts

@@ -16,11 +16,13 @@ export function createSetupInputs(
     checksum: "",
     downloadFromAstralMirror: false,
     enableCache: true,
+    exportPythonArch: false,
     githubToken: "",
     ignoreEmptyWorkdir: false,
     ignoreNothingToCache: false,
     noProject: false,
     pruneCache: false,
+    pythonArch: "",
     pythonDir: "/tmp/uv-python-dir",
     pythonVersion: "",
     quiet: false,