implement shopMail giftPackage function

Co-authored-by: Kinesis <CCasusensa@users.noreply.github.com>

src/main/java/emu/grasscutter/data/def/RewardBoxData.java

@@ -0,0 +1,27 @@
+package emu.grasscutter.data.def;
+
+import java.util.List;
+
+import emu.grasscutter.data.GameResource;
+import emu.grasscutter.data.ResourceType;
+import emu.grasscutter.data.common.RewardBoxItemData;
+
+@ResourceType(name = "RewardPreviewExcelConfigData.json")
+public class RewardBoxData extends GameResource {
+    public int Id;
+    public List<RewardBoxItemData> PreviewItems;
+
+    @Override
+    public int getId() {
+        return Id;
+    }
+
+    public List<RewardBoxItemData> getRewardBoxItemList() {
+        return PreviewItems;
+    }
+
+    @Override
+    public void onLoad() {
+
+    }
+}