Does json conversion yell when seeing unknown keys?

```bash
echo '{"name": "john"}\n{"surname": "landis"}' | cargo run -- from -f ndjson --sample-size 1 | xan v
```

This is tricky to do because it is less performant to do so. Might decrement a counter and only check remaining keys afterwards. Even so, we cannot really do it within the context of the DFS.