Hypothetical move logic doesn't always consider pawn special case

[dantb]

Hypothetical move logic doesn't always consider pawn special case

[dantb]

Instead of trying to wedge in a fake move executor driven by system level tests, I think it would be better to use this as an opportunity to implement the "loading" of board states. This can be done through chess algebraic notation.

Then the system tests for edge cases like this become a lot easier to implement, as they board state can be easily loaded.

[dantb]

The saving and loading of board states has been implemented, as well as all of the remaining rules of chess - this issue was fixed as an outcome of that.

Both cases mentioned above rely on the MoveIntoCheckValidator doing its job properly - it now does this and to ensure this doesn't regress I've added an integration test BlackKingBeforeMovingInFrontOfWhitePawn() in the system tests library.