feat: add configurable extension download fallback

lib/models/settings.dart

@@ -33,6 +33,7 @@ class AppSettings {
   final bool askQualityBeforeDownload;
   final bool enableLogging;
   final bool useExtensionProviders;
+  final List<String>? downloadFallbackExtensionIds;
   final String? searchProvider;
   final String? homeFeedProvider;
   final bool separateSingles;
@@ -108,6 +109,7 @@ class AppSettings {
     this.askQualityBeforeDownload = true,
     this.enableLogging = false,
     this.useExtensionProviders = true,
+    this.downloadFallbackExtensionIds,
     this.searchProvider,
     this.homeFeedProvider,
     this.separateSingles = false,
@@ -170,6 +172,8 @@ class AppSettings {
     bool? askQualityBeforeDownload,
     bool? enableLogging,
     bool? useExtensionProviders,
+    List<String>? downloadFallbackExtensionIds,
+    bool clearDownloadFallbackExtensionIds = false,
     String? searchProvider,
     bool clearSearchProvider = false,
     String? homeFeedProvider,
@@ -232,6 +236,9 @@ class AppSettings {
       enableLogging: enableLogging ?? this.enableLogging,
       useExtensionProviders:
           useExtensionProviders ?? this.useExtensionProviders,
+      downloadFallbackExtensionIds: clearDownloadFallbackExtensionIds
+          ? null
+          : (downloadFallbackExtensionIds ?? this.downloadFallbackExtensionIds),
       searchProvider: clearSearchProvider
           ? null
           : (searchProvider ?? this.searchProvider),

lib/models/settings.g.dart

@@ -35,6 +35,10 @@ AppSettings _$AppSettingsFromJson(Map<String, dynamic> json) => AppSettings(
   askQualityBeforeDownload: json['askQualityBeforeDownload'] as bool? ?? true,
   enableLogging: json['enableLogging'] as bool? ?? false,
   useExtensionProviders: json['useExtensionProviders'] as bool? ?? true,
+  downloadFallbackExtensionIds:
+      (json['downloadFallbackExtensionIds'] as List<dynamic>?)
+          ?.map((e) => e as String)
+          .toList(),
   searchProvider: json['searchProvider'] as String?,
   homeFeedProvider: json['homeFeedProvider'] as String?,
   separateSingles: json['separateSingles'] as bool? ?? false,
@@ -105,6 +109,7 @@ Map<String, dynamic> _$AppSettingsToJson(
   'askQualityBeforeDownload': instance.askQualityBeforeDownload,
   'enableLogging': instance.enableLogging,
   'useExtensionProviders': instance.useExtensionProviders,
+  'downloadFallbackExtensionIds': instance.downloadFallbackExtensionIds,
   'searchProvider': instance.searchProvider,
   'homeFeedProvider': instance.homeFeedProvider,
   'separateSingles': instance.separateSingles,