_id from findOne is not ObjectID

```js
it.only("", async () => {
await db.get("ttt").insert({ name: "bbb", otherId: new ObjectID() })
let a = await db.get("ttt").findOne({ name: "bbb" })
try {
expect(a._id instanceof ObjectID).true
expect(a.OtherId instanceof ObjectID).true
} catch (e) {
console.log(e)
}
})
```

Start with the JavaScript reproduction in issue #268 and trace the insert and findOne entry points to inspect the returned _id and otherId values. Verify the field names used by the assertion, then confirm that both returned identifiers are ObjectID instances.

Written by the indexing model from the issue text.