The strict provenance APIs are a better version of these, and things like `.addr()` work for the "that cast looks sketchy" case even if the full strict provenance stuff never happens.  So I think it's fine to move away from these, and encourage the others instead.

Changing to those doesn't introduce any new unsoundness over the existing ones, so they're the better "if you won't want to think about it" replacement.  But also mention the strict provenance APIs, as that's what we'd rather they use instead.