allow move arena to properly handle skipping a move

src/logic/move.rs

@@ -4,11 +4,8 @@ use lazy_static::lazy_static;
 
 #[derive(Clone, Debug)]
 pub struct Move {
-    /// `i` position of move
-    pub i: usize,
-
-    /// `j` position of move
-    pub j: usize,
+    /// Coordinates (i, j) of the move (if it exists)
+    pub coord: Option<(usize, usize)>,
 
     /// [`Board`] state after move is made
     pub board: Board,
@@ -43,10 +40,14 @@ lazy_static! {
 }
 
 impl Move {
-    pub fn new(i: usize, j: usize, board: Board, color: Piece, agent_color: Piece) -> Self {
+    pub fn new(
+        coord: Option<(usize, usize)>,
+        board: Board,
+        color: Piece,
+        agent_color: Piece,
+    ) -> Self {
         let mut m = Move {
-            i,
-            j,
+            coord,
             board,
             winner: board.game_winner(),
             parent: None,
@@ -61,10 +62,6 @@ impl Move {
         m
     }
 
-    pub const fn coords(&self) -> (usize, usize) {
-        (self.i, self.j)
-    }
-
     fn compute_self_value(&self, agent_color: Piece) -> i64 {
         if self.winner == Winner::Player(!agent_color) {
             // if this board results in the opponent winning, MAJORLY negatively weigh this move