fix(download): name variants by measured quality

lib/services/download_request_payload.dart

@@ -49,6 +49,7 @@ class DownloadRequestPayload {
   final bool deferSafPublish;
   final bool requiresContainerConversion;
   final bool allowQualityVariant;
+  final String qualityVariant;
   final String songLinkRegion;
 
   const DownloadRequestPayload({
@@ -100,6 +101,7 @@ class DownloadRequestPayload {
     this.deferSafPublish = false,
     this.requiresContainerConversion = false,
     this.allowQualityVariant = false,
+    this.qualityVariant = '',
     this.songLinkRegion = 'US',
   });
 
@@ -153,6 +155,7 @@ class DownloadRequestPayload {
       'defer_saf_publish': deferSafPublish,
       'requires_container_conversion': requiresContainerConversion,
       'allow_quality_variant': allowQualityVariant,
+      'quality_variant': qualityVariant,
       'songlink_region': songLinkRegion,
     };
   }
@@ -210,6 +213,7 @@ class DownloadRequestPayload {
       deferSafPublish: deferSafPublish,
       requiresContainerConversion: requiresContainerConversion,
       allowQualityVariant: allowQualityVariant,
+      qualityVariant: qualityVariant,
       songLinkRegion: songLinkRegion,
     );
   }

lib/services/platform_bridge.dart

@@ -642,6 +642,24 @@ class PlatformBridge {
     return result as String?;
   }
 
+  static Future<Map<String, dynamic>> createUniqueSafFileFromPath({
+    required String treeUri,
+    required String relativeDir,
+    required String fileName,
+    required String mimeType,
+    required String srcPath,
+    String preservedSuffix = '',
+  }) {
+    return _invokeMap('safCreateUniqueFromPath', {
+      'tree_uri': treeUri,
+      'relative_dir': relativeDir,
+      'file_name': fileName,
+      'mime_type': mimeType,
+      'src_path': srcPath,
+      'preserved_suffix': preservedSuffix,
+    });
+  }
+
   static Future<void> openContentUri(String uri, {String mimeType = ''}) async {
     await _channel.invokeMethod('openContentUri', {
       'uri': uri,