Implement convert gem handler

src/main/java/emu/nebula/server/handlers/HandlerGemConvertReq.java

@@ -0,0 +1,28 @@
+package emu.nebula.server.handlers;
+
+import emu.nebula.net.NetHandler;
+import emu.nebula.net.NetMsgId;
+import emu.nebula.proto.Public.UI32;
+import emu.nebula.net.HandlerId;
+import emu.nebula.net.GameSession;
+
+@HandlerId(NetMsgId.gem_convert_req)
+public class HandlerGemConvertReq extends NetHandler {
+
+    @Override
+    public byte[] handle(GameSession session, byte[] message) throws Exception {
+        // Parse request
+        var req = UI32.parseFrom(message);
+        
+        // Convert gems
+        var change = session.getPlayer().getInventory().convertGems(req.getValue());
+        
+        if (change == null) {
+            return session.encodeMsg(NetMsgId.gem_convert_failed_ack);
+        }
+        
+        // Encode and send
+        return session.encodeMsg(NetMsgId.gem_convert_succeed_ack, change.toProto());
+    }
+
+}