Fix windows build cannot find versions.py

When I install executorch on windows I run into this error:   error:
[Errno 2] No such file or directory:
'pip-out\\lib.win-amd64-cpython-312\\executorch\\version.py'

It turns out sometimes the dst directory (in this case
pip-out\lib.win-amd64-cpython-312\executorch) is not installed before we
write version.py into it. This PR adds a mkpath call to make sure it's
always there.

Author: larryliu0820

setup.py

@@ -635,6 +635,9 @@ def run(self):
             dst_root = self.get_package_dir(".")
         else:
             dst_root = os.path.join(self.build_lib, "executorch")
+            # On Windows the package directory might not exist yet when building from a
+            # clean tree. Ensure it is created before we attempt to write version.py.
+            self.mkpath(dst_root)
         # Create the version file.
         Version.write_to_python_file(os.path.join(dst_root, "version.py"))