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.

dist/save-cache/index.cjs

@@ -64447,6 +64447,9 @@ function loadInputs() {
   const version3 = getInput("version");
   const versionFile = getVersionFile(workingDirectory);
   const pythonVersion = getPythonVersion(versionFile);
+  const pythonArchInput = getInput("python-arch");
+  const pythonArch = pythonArchInput || process.env.UV_PYTHON_ARCH || "";
+  const exportPythonArch = pythonArchInput !== "";
   const activateEnvironment = getBooleanInput("activate-environment");
   const noProject = getBooleanInput("no-project");
   const venvPath = getVenvPath(workingDirectory, activateEnvironment);
@@ -64484,12 +64487,14 @@ function loadInputs() {
     checksum,
     downloadFromAstralMirror,
     enableCache,
+    exportPythonArch,
     githubToken,
     ignoreEmptyWorkdir,
     ignoreNothingToCache,
     manifestFile,
     noProject,
     pruneCache: pruneCache2,
+    pythonArch,
     pythonDir,
     pythonVersion,
     quiet: quiet2,