cleanup stuff related to move legality checks and attack checks

[Sopel97]

• in chess_pos_db_ we have to cleanup some stuff related to move/position legality checks.

  • in particular Board::isKingAttackedAfterMove, Board::isSquareAttackedAfterMove need better implementations

  • Board::isSquareAttacked shouldn't have the 'captured' and 'occupied' parameter

  • remove this assert https://github.com/Sopel97/chess_pos_db/blob/master/src/chess/Position.cpp#L26

  • overall all predicates that chess whether something is attacked now or after a move need to be rethought and reimplemented.

  • what we need (all of these happen to not require pos state info so they may be implemented in board only):

    • pos/board.isSquareAttacked(Square, Color attacker)
    • pos/board.isSquareAttackedAfterMove(Square, Move, Color attacker)
    • pos/board.isPieceAttacked(Square) - similar to isSquareAttacked but attacker depends on the piece color. false if empty
    • pos/board.isPieceAttackedAfterMove(Square pieceSq, Move) - false if empty
    • pos/board.createsDiscoveredAttackOnOwnKing(Move) - attacker color opposite to color of the piece being moved
    • pos/board.createsAttackOnOwnKing(Move) - calls board.isPieceAttackedAfterMove(ksq, Move)
    • pos/board.attackers(Square)
    • pos/board.attacks(Square) - empty bitboard if square empty

  • additionally we may want

    • pos.isMoveLegal(Move) - this would take ANY move, not just a pseudoLegalMove
    • pos.isPseudoLegalMoveLegal(Move) - like it is in movegen now
    • pos.isMovePseudoLegal(Move) - takes ANY move