enable unreachable_pub lint

This causes some other lints to start firing too (which is good), but
I'm going to fix them in follow-up commits to keep things organized.

src/service/rooms/state/data.rs

@@ -3,7 +3,7 @@ use ruma::{EventId, OwnedEventId, RoomId};
 use std::{collections::HashSet, sync::Arc};
 use tokio::sync::MutexGuard;
 
-pub trait Data: Send + Sync {
+pub(crate) trait Data: Send + Sync {
     /// Returns the last state hash key added to the db for the given room.
     fn get_room_shortstatehash(&self, room_id: &RoomId) -> Result<Option<u64>>;