public static BitBoard BitBoardRank(this Square sq) => RankBB[sq.Rank().AsInt()];
public static bool IsValidEp(this Square s) => s.Rank() == ERank.Rank3 || s.Rank() == ERank.Rank6;
public static char RankChar(this Square s) => s.Rank().RankChar();
public static Rank RelativeRank(this Square s, Player color) => s.Rank().RelativeRank(color);