[feature request]: flat NestedJSON

type NestedJSON = {
  user: {
    id: number;
    profile: {
      firstName?: string;
      lastName: string;
    };
    metadata: {
      createdAt?: string | null;
      source: string;
    };
  };
};

type Result = FlattenLeafs<NestedJSON>;

type Result = {
  "user.id": number;
  "user.profile.lastName": string;
  "user.metadata.source": string;
  "user.profile.firstName"?: string | undefined;
  "user.metadata.createdAt"?: string | null | undefined;
}