feat(game): enhance game engine with resign functionality and optimize move generation

modules/core/src/main/resources/keys/public.pem

@@ -0,0 +1,9 @@
+-----BEGIN PUBLIC KEY-----
+MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAxDsnsCAl0vQx7Vu9CLDZ
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+634g7mgsPZAQ9PJEsv4Qvm05T9L6+Gmq6N3bMVLKRXs4RhDhaFbYH9GtUg1eI0yH
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+7dhFeNVWzQ2m53eOhBzNQX+v3pgjVStsePhBRt2LyGfwkNzmqDgqWsMzSHRMY+cn
+WQIDAQAB
+-----END PUBLIC KEY-----

modules/core/src/main/scala/de/nowchess/chess/engine/GameEngine.scala

@@ -142,6 +142,8 @@ class GameEngine(
   def redo(): Unit = synchronized(performRedo())
 
   /** Resign from the game. The opponent wins. */
+  def resign(): Unit = synchronized(resign(currentContext.turn))
+
   def resign(color: Color): Unit = synchronized {
     if currentContext.result.isDefined then
       notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.GameAlreadyOver))
@@ -150,7 +152,7 @@ class GameEngine(
       pendingDrawOffer = None
       stopClock()
       invoker.clear()
-      notifyObservers(ResignEvent(currentContext, color.opposite))
+      notifyObservers(ResignEvent(currentContext, color))
   }
 
   /** Offer a draw. */