Made FramedPacket immutable

src/main/java/net/minestom/server/network/netty/codec/GroupedPacketHandler.java

@@ -13,7 +13,7 @@ public class GroupedPacketHandler extends MessageToByteEncoder<FramedPacket> {
 
     @Override
     protected ByteBuf allocateBuffer(ChannelHandlerContext ctx, FramedPacket msg, boolean preferDirect) {
-        return msg.body.retainedSlice();
+        return msg.getBody().retainedSlice();
     }
 
 }

src/main/java/net/minestom/server/network/netty/packet/FramedPacket.java

@@ -9,10 +9,14 @@ import org.jetbrains.annotations.NotNull;
  */
 public class FramedPacket {
 
-    public final ByteBuf body;
+    private final ByteBuf body;
 
     public FramedPacket(@NotNull ByteBuf body) {
         this.body = body;
     }
 
+    @NotNull
+    public ByteBuf getBody() {
+        return body;
+    }
 }