devalue: Malformed null-prototype object keys bypass __proto__ rejection via property-key coercion

Summary

This is another instance of https://github.com/sveltejs/devalue/security/advisories/GHSA-mwv9-gp5h-frr4, where some payloads could cause `parse` to create objects with a `__proto__` own property. This on its own is not enough to cause prototype pollution, and indeed this is actually how `JSON.parse` works, but we decided to be a little more defensive here and not allow the creation of objects with `__proto__` own-properties. It is very unlikely for this to cause any issues.