`ShardingInfo` is public

[sylwiaszunejko]

The ShardingInfo class and most of its method and properties are public. I don't see a good reason for that. It is only used in internal classes. Can we break the API and change its visibility? Or is there some use case to having it public?

[sylwiaszunejko]

@dkropachev FYI

[wprzytula]

The case is similar for Lwt* items, IIRC.