refactor: move blob_storage_handler.dart and add download feature

app/lib/util/multimodal/persistent_storage_handler.dart

@@ -5,7 +5,7 @@ import 'dart:typed_data';
 import 'package:cross_file/cross_file.dart';
 import 'package:path/path.dart' as path;
 import 'package:path_provider/path_provider.dart';
-import 'blob_storage_handler.dart';
+import 'package:studyu_core/core.dart';
 import 'encrypted_audio_file.dart';
 import 'encrypter_handler.dart';
 

app/lib/util/multimodal/blob_storage_handler.dart → core/lib/src/util/multimodal/blob_storage_handler.dart

@@ -1,4 +1,5 @@
 import 'dart:io';
+import 'dart:typed_data';
 
 import 'package:studyu_core/env.dart' as env;
 
@@ -9,4 +10,8 @@ class BlobStorageHandler {
     // we use uploadBinary instead of upload until this is fixed: https://github.com/supabase/supabase-flutter/issues/685
     await env.client.storage.from(_observationsBucketName).uploadBinary(aFileName, aFile.readAsBytesSync());
   }
+
+  Future<Uint8List> downloadObservation(String aFile) async {
+    return await env.client.storage.from(_observationsBucketName).download(aFile);
+  }
 }

core/lib/src/util/util.dart

@@ -1,2 +1,3 @@
 export 'extensions.dart';
+export 'multimodal/blob_storage_handler.dart';
 export 'supabase_object.dart';