CI(macOS): retry flaky hdiutil DMG creation; delete per-arch bundles only on success

scripts/retry.sh

@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+# Sourceable helper: `retry <cmd...>` runs a command, retrying up to 3 times
+# with a 5-minute wait between attempts. Useful for flaky commands such as
+# `hdiutil create` intermittently failing with "Resource busy".
+retry() {
+  local attempt=1 max_attempts=3 delay=300
+  until "$@"; do
+    if [ "$attempt" -ge "$max_attempts" ]; then
+      echo "::error::Command failed after $attempt attempts: $*"
+      return 1
+    fi
+    echo "Attempt $attempt failed: $*. Retrying in $((delay / 60)) minutes..."
+    sleep "$delay"
+    attempt=$((attempt + 1))
+  done
+}