fix: don't search drawn positions (#168)

Elo   | 28.62 +- 10.58 (95%)
SPRT  | 8.0+0.08s Threads=1 Hash=16MB
LLR   | 3.00 (-2.94, 2.94) [-5.00, 0.00]
Games | N: 1472 W: 349 L: 228 D: 895
Penta | [19, 120, 346, 223, 28]
https://openbench.nocturn9x.space/test/4812/

bench: 1119492

Author: DeveloperPaul123

engine/src/search.rs

@@ -425,6 +425,11 @@ impl<'a, Log: LogLevel> Search<'a, Log> {
             return score;
         }
 
+        // don't bother searching if the board is in a draw state
+        if board.is_draw() {
+            return Score::DRAW;
+        }
+
         // get all legal moves
         let mut move_list = MoveList::new();
         let mut order_list = ArrayVec::<MoveOrder, MAX_MOVE_LIST_SIZE>::new();