Gets the :class:`piece <chess.Piece>` at the given square.

def piece_at(self, square: Square) -> Optional[Piece]:
        """Gets the :class:`piece <chess.Piece>` at the given square."""
        piece_type = self.piece_type_at(square)
        if piece_type:
            mask = BB_SQUARES[square]
            color = bool(self.occupied_co[WHITE] & mask)
            return Piece(piece_type, color)
        else:
            return None