Avoid duplicating objects.

**Question**
How to avoid duplicating objects in datastore?
What is the best practice let Hive know that the object must be overridden or ignored instead of duplicating.

**Code sample**
Future addCountries(List countries) async {
final Box box = await openDataBox();
box.addAll(countries);
}

Future> getCountries() async {
final List countries = [];
final Box box = await openDataBox();
countries.addAll(box.values.toList());
return countries;
}

**Version**
- Platform: iOS, Android, Web
- Flutter version: [ 2.5.3]
- Hive version: [2.0.4]

```[tasklist]
### Tasks
- [ ] https://github.com/isar/hive/issues/1261
```

Start with the addCountries and getCountries entry points shown in the issue, then review the linked task #1261 for the current direction. The issue is complete only once the intended behavior for existing objects—override, ignore, or another policy—is decided and clearly documented or implemented.

Written by the indexing model from the issue text.