feat(draw by fifty moves) : DONE

- create a new function to check if it's a draw by fifty moves rule or not.
- this will help UI devs to show exact reason of a draw.

Author: HarshilSySCreations

Diff for: src/chess.ts

@@ -1086,16 +1086,20 @@ export class Chess {
     return this._getPositionCount(this.fen()) >= 3
   }
 
-  isDraw() {
+  isDrawByFiftyMoves(): boolean {
+    return this._halfMoves >= 100 // 50 moves per side = 100 half moves
+  }
+
+  isDraw(): boolean {
     return (
-      this._halfMoves >= 100 || // 50 moves per side = 100 half moves
+      this.isDrawByFiftyMoves() ||
       this.isStalemate() ||
       this.isInsufficientMaterial() ||
       this.isThreefoldRepetition()
     )
   }
 
-  isGameOver() {
+  isGameOver(): boolean {
     return this.isCheckmate() || this.isStalemate() || this.isDraw()
   }