rpc: add node tier information to matched orders in BatchSnapshot

By exposing these values, traders can start to get a better idea of the cost gap between a t0 vs t1 channel as defined now.

Start at the RPC definition and implementation for BatchSnapshot, then trace how matched orders are assembled. Identify the existing node-related values available for each matched order and confirm the intended t0 and t1 tier representation. Done means the BatchSnapshot response exposes node tier information for matched orders and the relevant RPC behavior is covered by tests, if present.

Written by the indexing model from the issue text.