Thank you for reaching out to us.
Kindly note that our custom data source API example on GitHub is a sample project not optimized for production. Since the sample server is created to illustrate the main steps of implementing custom data source API protocol, it doesn't contain a lot of features, as well as Top-N and Bottom-N filters. However, it is possible to implement the mentioned filters in your own server implementation using any approach you like.
Hope you will find our answer helpful.