Changes

* Two of the migrations work on the format of stored state (local storage and prefs)

* During a dry-run-only test of Default Provider Selection, an underlying bug was triggered that caused clients to effectively DDoS NextDNS's endpoint. In the aftermath, a new endpoint was set up and we have a migration to convert occurrences of the old endpoint in stored URI values to the new one.

== Prefs ==

* TODO: list all involved prefs and semantics.