feat(game): add self-play game loop

Game.scala

@@ -0,0 +1,60 @@
+package gambit
+
+object Game:
+  final case class Outcome(
+      moves: List[String],
+      result: String,
+      plies: Int,
+      moveInts: List[Int],
+      startFen: String
+  )
+
+  def selfPlay(startFen: String, maxPlies: Int, depth: Int, timeMs: Long): Outcome =
+    val pos = Fen.parse(startFen)
+    val searcher = new Searcher
+    val history = scala.collection.mutable.ArrayBuffer[Long](pos.hash)
+    val played = scala.collection.mutable.ListBuffer[String]()
+    val ints = scala.collection.mutable.ListBuffer[Int]()
+    var result = "adjudicated draw (ply limit)"
+    var over = false
+
+    while !over && played.size < maxPlies do
+      val legal = new MoveList()
+      MoveGen.generateLegal(pos, legal)
+      if legal.size == 0 then
+        result =
+          if pos.inCheck(pos.sideToMove) then
+            if pos.sideToMove == Color.White then "0-1 (black mates)" else "1-0 (white mates)"
+          else "1/2-1/2 (stalemate)"
+        over = true
+      else if Draw.isFiftyMove(pos) then
+        result = "1/2-1/2 (fifty-move rule)"
+        over = true
+      else if Draw.isInsufficientMaterial(pos) then
+        result = "1/2-1/2 (insufficient material)"
+        over = true
+      else if Draw.isThreefold(history, pos.hash) then
+        result = "1/2-1/2 (threefold repetition)"
+        over = true
+      else
+        searcher.setGameHistory(history.toArray, history.size - 1)
+        val r = searcher.search(pos, depth, timeMs)
+        if r.bestMove == 0 then
+          result = "aborted (no move)"
+          over = true
+        else
+          played += Move.uci(r.bestMove)
+          ints += r.bestMove
+          pos.make(r.bestMove)
+          history += pos.hash
+
+    Outcome(played.toList, result, played.size, ints.toList, startFen)
+
+  def resultToken(result: String): String =
+    if result.startsWith("1-0") then "1-0"
+    else if result.startsWith("0-1") then "0-1"
+    else if result.startsWith("1/2") || result.contains("draw") then "1/2-1/2"
+    else "*"
+
+  def pgn(outcome: Outcome): String =
+    Pgn.write(outcome.startFen, outcome.moveInts, resultToken(outcome.result))