tor-hsservice: Add `RunningOnionService` API

As discussed in #1227 (closed), I'm adding a separate RunningOnionService for representing running OnionServices. OnionService is now the ConfiguredOnionService type mentioned in #1227 (closed).

The new version of OnionService also has an onion_name() function, which I'm using to implement the arti hss onion-name command (it was previously implemented using StateMgr::onion_name()). Since the arti crate doesn't have access to many of the types needed for building OnionService, I ended up adding a create_onion_service function to TorClient (I'm not entirely convinced it belongs in TorClient though..). I also removed the (badly named) state module I added in !1837 (merged)

Closes #1227 (closed)