Support atomic directory promotion across platforms

internal/fileops/rename_noreplace_darwin.go

@@ -0,0 +1,11 @@
+//go:build darwin
+
+package fileops
+
+import "golang.org/x/sys/unix"
+
+func checkAtomicDirectoryPromotionSupport() error { return nil }
+
+func renameDirectoryNoReplace(src, dst string) error {
+	return unix.RenamexNp(src, dst, unix.RENAME_EXCL)
+}