Add rarity points

[erwan-joly]

Add rarity points
Add rarity rates

        public int RarityPoint(short rarity, short lvl)
        {
            var p = rarity switch
            {
                0 => 0,
                1 => 1,
                2 => 2,
                3 => 3,
                4 => 4,
                5 => 5,
                6 => 7,
                7 => 10,
                8 => 15,
                _ => rarity * 2,
            };
            return p * (lvl / 5 + 1);
        }