exists<_Model extends _RepositoryModel>  method 
Check if a _Model is accessible locally.
First checks if there's a matching query in memoryCacheProvider and then check sqliteProvider.
Does not query remoteProvider.
Implementation
Future<bool> exists<_Model extends _RepositoryModel>({
  Query? query,
}) async {
  if (memoryCacheProvider.canFind<_Model>(query)) {
    final results = memoryCacheProvider.get<_Model>(query: query, repository: this);
    return results?.isNotEmpty ?? false;
  }
  return await sqliteProvider.exists<_Model>(query: query, repository: this);
}