rookCastlesTo function
Returns the square the rook moves to when castling.
Implementation
Square rookCastlesTo(Side side, CastlingSide cs) => switch (side) {
Side.white => switch (cs) {
CastlingSide.queen => Square.d1,
CastlingSide.king => Square.f1,
},
Side.black => switch (cs) {
CastlingSide.queen => Square.d8,
CastlingSide.king => Square.f8,
},
};