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.

test/models/livetv_flexible_parsing_test.dart

@@ -1,8 +1,5 @@
 import 'package:flutter_test/flutter_test.dart';
 import 'package:plezy/models/livetv_dvr.dart';
-import 'package:plezy/models/livetv_lineup.dart';
-import 'package:plezy/models/media_grabber_device.dart';
-import 'package:plezy/models/media_provider_info.dart';
 import 'package:plezy/models/media_subscription.dart';
 
 void main() {
@@ -28,48 +25,6 @@ void main() {
       {'uuid': 'device-1'},
     ]);
 
-    final grabber = MediaGrabberDevice.fromJson({
-      'key': 'device-1',
-      'uuid': 'device-1',
-      'ChannelMapping': [
-        {'channelKey': 7},
-        {'channelKey': 'channel-1'},
-      ],
-      'Setting': [
-        {'id': 7},
-        {'id': 'setting-1'},
-      ],
-    });
-    expect(grabber.channelMappings.map((entry) => entry.channelKey), ['channel-1']);
-    expect(grabber.settings.map((entry) => entry.id), ['setting-1']);
-
-    final lineup = LiveTvLineup.fromJson({
-      'uuid': 'lineup-1',
-      'Channel': [
-        {'callSign': 7},
-        {'key': 'channel-1', 'callSign': 'ONE'},
-      ],
-    });
-    expect(lineup.channels.map((entry) => entry.callSign), ['ONE']);
-
-    final provider = MediaProviderInfo.fromJson({
-      'identifier': 'provider-1',
-      'Feature': [
-        {'type': 7},
-        {
-          'type': 'livetv',
-          'Directory': [
-            'invalid',
-            {'key': 'guide'},
-          ],
-        },
-      ],
-    });
-    expect(provider.features.map((entry) => entry.type), ['livetv']);
-    expect(provider.features.single.directories, [
-      {'key': 'guide'},
-    ]);
-
     final template = SubscriptionTemplate.fromJson({
       'MediaSubscription': [
         {'title': 7},