refactor: remove unreachable code paths and unused members

Drops dead code across services, models, utils and widgets, including the
connection auth service, which had no implementer, and the Live TV DVR
provisioning models, which had no caller.

Tests that only covered deleted behaviour are removed or trimmed. No
behaviour change.

lib/services/plex_api_cache.dart

@@ -1,6 +1,7 @@
 import '../media/ids.dart';
 
 import 'package:drift/drift.dart';
+import 'package:flutter/foundation.dart';
 
 import '../database/app_database.dart';
 import '../database/plex_metadata_recovery.dart';
@@ -73,6 +74,7 @@ class PlexApiCache extends ApiCache {
   // Rating keys can be alphanumeric, not just numeric.
   static final RegExp _metadataKeyPattern = RegExp(r'/library/metadata/([^/]+)$');
 
+  @visibleForTesting
   Future<Set<String>> getPinnedKeys(ServerId serverId) => extractPinnedIds(serverId, _metadataKeyPattern);
 
   /// Copy one pinned item between cache namespaces.