dev: Added QS/KS castle checking; simplified moveList pruning

Piece.cpp

@@ -126,10 +126,9 @@ std::vector<Move> King::getLegalMoves(const Square &from, const Board &board) co
     // will this actually work?
     moveList.erase(
             std::remove_if(moveList.begin(), moveList.end(),
-                           [&](const Square &x) {
-                               return std::find(x.begin(), x.end(), !x.isValid()) != x.end();
-                           }),
-                           moveList.end());
+                           [&](const auto &x) {
+                               return !x.to.isValid();
+                           }));
     return moveList;
 }