improve: copy MerchantRecipe of TradeCause

StockEvents are called on different threads, so we need to copy MerchantRecipe to avoid unexpected changes.

src/main/java/net/okocraft/boxtradestick/TradeProcessor.java

@@ -138,7 +138,7 @@ private static boolean trade0(@NotNull Player trader, @NotNull AbstractVillager
         }
 
         var stockHolder = BoxAPI.api().getBoxPlayerMap().get(trader).getCurrentStockHolder();
-        var cause = new TradeCause(trader, merchantOffer);
+        var cause = new TradeCause(trader, new MerchantRecipe(merchantOffer));
 
         if (stockHolder.decreaseIfPossible(ingredientMap, cause)) {
             var resultBukkit = merchantOffer.getResult();