DOMPurify: Permanent `ALLOWED_ATTR` pollution via `setConfig()` bypassing the hook clone-guard (incomplete fix of the 3.4.7 hook-pollution patch)

Summary DOMPurify 3.4.7 shipped a security fix "permanent hook pollution" that makes a registered uponSanitizeAttribute hook's mutation of data.allowedAttributes non-persistent — so allowing an attribute for one element does not leak into later sanitize calls. The fix clones ALLOWEDATTR inside...