feature(mobile): hash assets & sync via checksum (#2592)

* compare different sha1 implementations

* remove openssl sha1

* sync via checksum

* hash assets in batches

* hash in background, show spinner in tab

* undo tmp changes

* migrate by clearing assets

* ignore duplicate assets

* error handling

* trigger sync/merge after download and update view

* review feedback improvements

* hash in background isolate on iOS

* rework linking assets with existing from DB

* fine-grained errors on unique index violation

* hash lenth validation

* revert compute in background on iOS

* ignore duplicate assets on device

* fix bug with batching based on accumulated size

---------

Co-authored-by: Fynn Petersen-Frey <zoodyy@users.noreply.github.com>

mobile/lib/modules/backup/background_service/background.service.dart

@@ -132,6 +132,17 @@ class BackgroundService {
     }
   }
 
+  Future<Uint8List?> digestFile(String path) {
+    return _foregroundChannel.invokeMethod<Uint8List>("digestFile", [path]);
+  }
+
+  Future<List<Uint8List?>?> digestFiles(List<String> paths) {
+    return _foregroundChannel.invokeListMethod<Uint8List?>(
+      "digestFiles",
+      paths,
+    );
+  }
+
   /// Updates the notification shown by the background service
   Future<bool?> _updateNotification({
     String? title,