Issue with Parsing Nested JSON Fields with the Same Key Name in

### Problem Description:
I am encountering an issue with parsing nested JSON fields using json_serializable in Dart. Below is the JSON structure I am receiving:

```
{
is_admin: false,
profiles: {
id: f13b4125-30bf-4dd2-8331-e1a7066bdd1b,
username: antek2
}
}
```

I am trying to extract both the id and username fields from the nested profiles object using the following freezed class:

```
@freezed
class GroupMember with _$GroupMember {
const GroupMember._();
const factory GroupMember({
@JsonKey(name: 'profiles') @_IdConverter() required String id,
@JsonKey(name: 'profiles') @_UsernameConverter() required String username,
@JsonKey(name: 'is_admin') required bool isAdmin,
}) = _GroupMember;

factory GroupMember.fromJson(Map json) =>
_$GroupMemberFromJson(json);
}
```

he problem arises when I attempt to define two fields (id and username) with the same @ JsonKey(name: 'profiles') annotation. This results in the following error:

`More than one field has the JSON key for name "profiles".`

### Questions
1. Is there a proper way to handle such cases where multiple values need to be extracted from a single nested object?
2. Would this be a feasible update for the json_serializable package to support such scenarios? If so, I would be happy to contribute and attempt a fix for this functionality.

### Additional Context
While I have implemented custom converters (_IdConverter and _UsernameConverter) to handle the extraction, the limitation of having only one field with the same JSON key name makes this approach impractical. I am looking for a cleaner and more intuitive solution.

Let me know your thoughts on this issue. Any guidance or recommendations for best practices would be greatly appreciated!