Framework / support structure for online -> offline routing fallback

In some scenarios, it would be nice to have a fallback to (or maybe even selectively prefer?) offline routing, such as when the user is in a poor network zone.

Off the top of my head, I'd say maybe we can have a fallback order or something and allow multiple route adapters in sequence. The offline routing would of course be the responsibility of the library end user, as routing itself is out of scope in Ferrostar, but it should support this use case.