[board] Implement ply and full move counters on Position

Pipe these numbers through the Builders

board/src/position/builders/position_builder.rs

@@ -16,6 +16,8 @@ pub struct Builder {
     flags: Flags,
     pieces: BTreeMap<Square, Piece>,
     kings: [Square; 2],
+    ply_counter: u16,
+    move_number: u16,
 }
 
 impl Builder {
@@ -28,6 +30,16 @@ impl Builder {
         self
     }
 
+    pub fn ply_counter(&mut self, num: u16) -> &mut Self {
+        self.ply_counter = num;
+        self
+    }
+
+    pub fn move_number(&mut self, num: u16) -> &mut Self {
+        self.move_number = num;
+        self
+    }
+
     pub fn place_piece(&mut self, piece: PlacedPiece) -> &mut Self {
         let square = piece.square();
 
@@ -50,7 +62,14 @@ impl Builder {
                 .filter(Self::is_piece_placement_valid),
         );
 
-        Position::new(self.player_to_move, self.flags, pieces, None)
+        Position::new(
+            self.player_to_move,
+            self.flags,
+            pieces,
+            None,
+            self.ply_counter,
+            self.move_number,
+        )
     }
 }
 
@@ -82,6 +101,8 @@ impl Default for Builder {
             flags: Flags::default(),
             pieces: pieces,
             kings: [white_king_square, black_king_square],
+            ply_counter: 0,
+            move_number: 1,
         }
     }
 }