Add `En Passant` implementation for pawns

[zkayser]

Acceptance Criteria:

1. The capturing pawn must have advanced exactly three ranks to perform this move.
2. The captured pawn must have moved two squares in one move, landing right next to the capturing pawn.
3. The en passant capture must be performed on the turn immediately after the pawn being captured moves. If the player does not capture en passant on that turn, they no longer can do it later.
4. This type of capture cannot happen if the capturing pawn has already advanced four or more squares. Another instance where this capture is not allowed is when the enemy pawn lands right next to your pawn but only after making two moves.