Method GetTopScores
GetTopScores(string, string, int, Action<List<LeaderboardEntry>>, Action<Exception>)
Fetches the top topCount entries ordered by score descending,
then by UpdatedAt ascending to break ties (earlier submissions rank higher).
public static void GetTopScores(string leaderboardName, string scoreName, int topCount, Action<List<LeaderboardEntry>> onSuccess, Action<Exception> onError = null)