cache cpython install on macos

cibuildwheel/macos.py

@@ -139,7 +139,7 @@ def get_python_configurations(
     return python_configurations
 
 
-def install_cpython(tmp: Path, version: str, url: str, free_threading: bool) -> Path:
+def install_cpython(_tmp: Path, version: str, url: str, free_threading: bool) -> Path:
     ft = "T" if free_threading else ""
     installation_path = Path(f"/Library/Frameworks/Python{ft}.framework/Versions/{version}")
     with FileLock(CIBW_CACHE_PATH / f"cpython{version}.lock"):
@@ -161,10 +161,10 @@ def install_cpython(tmp: Path, version: str, url: str, free_threading: bool) ->
                     """
                 )
                 raise errors.FatalError(msg)
-            pkg_path = tmp / "Python.pkg"
-            # download the pkg
-            download(url, pkg_path)
-            # install
+            python_filename = url.split("/")[-1]
+            pkg_path = CIBW_CACHE_PATH.joinpath("python", python_filename)
+            if not pkg_path.exists():
+                download(url, pkg_path)
             args = []
             if version.startswith("3.13"):
                 # Python 3.13 is the first version to have a free-threading option