* Add an AccountProvider type and use it within AppSettings.
* Use the AccountProvider type within the Authentication flow too.
* Fix unit test compilation with Swift 6.4
* Make sure defaultAccountProvider takes allowOtherAccountProviders into account.
* Document a caveat on using AuthenticationService.homeserver.value.accountProvider.
* swift 6 support for NSE and concurrency safe implementations for it
* enforcing required Sendable conformance for swift 6 migration in NSE
* use Mutex to access the string builder cache
* use an async stream to update timeline items diffs
* fix for Sendable appHooks
Doug
Mauro
Doug