Server.Servicet represents a gRPC service with potentially multiple rpcs and the information needed to route to them.
val v : unit -> tv () creates a new service
add_rpc ~name ~rpc t adds rpc to t and ensures that t can route to it with name.
val handle_request : t -> H2.Reqd.t -> unithandle_request t reqd handles routing reqd to the correct rpc if available in t.