feat(rules): add draw detection

Draw.scala

@@ -0,0 +1,24 @@
+package gambit
+
+object Draw:
+  def isFiftyMove(pos: Position): Boolean = pos.halfmove >= 100
+
+  def isInsufficientMaterial(pos: Position): Boolean =
+    var minors = 0
+    var sq = 0
+    while sq < 128 do
+      if Square.onBoard(sq) then
+        Piece.typeOf(pos.board(sq)) match
+          case Piece.Pawn | Piece.Rook | Piece.Queen => return false
+          case Piece.Knight | Piece.Bishop           => minors += 1
+          case _                                      => ()
+      sq += 1
+    minors <= 1
+
+  def isThreefold(history: collection.Seq[Long], current: Long): Boolean =
+    var count = 0
+    var i = 0
+    while i < history.length do
+      if history(i) == current then count += 1
+      i += 1
+    count >= 3