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/models/plex/plex_home.dart

@@ -37,18 +37,4 @@ class PlexHome {
   Map<String, dynamic> toJson() => _$PlexHomeToJson(this);
 
   PlexHomeUser? get adminUser => users.where((user) => user.admin).firstOrNull;
-
-  List<PlexHomeUser> get managedUsers => users.where((user) => !user.admin).toList();
-
-  List<PlexHomeUser> get restrictedUsers => users.where((user) => user.restricted).toList();
-
-  PlexHomeUser? getUserByUUID(String uuid) {
-    try {
-      return users.firstWhere((user) => user.uuid == uuid);
-    } catch (e) {
-      return null;
-    }
-  }
-
-  bool get hasMultipleUsers => users.length > 1;
 }

lib/models/plex/plex_video_playback_data.dart

@@ -26,6 +26,4 @@ class PlexVideoPlaybackData {
   });
 
   bool get hasValidVideoUrl => videoUrl != null && videoUrl!.isNotEmpty;
-
-  bool get hasMediaInfo => mediaInfo != null;
 }