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/asset_viewer/ui/top_control_app_bar.dart

@@ -72,15 +72,7 @@ class TopControlAppBar extends HookConsumerWidget {
                     color: Colors.grey[200],
                   ),
           ),
-        if (!asset.isLocal)
-          IconButton(
-            onPressed: onDownloadPressed,
-            icon: Icon(
-              Icons.cloud_download_outlined,
-              color: Colors.grey[200],
-            ),
-          ),
-        if (asset.storage == AssetState.merged)
+        if (asset.storage == AssetState.remote)
           IconButton(
             onPressed: onDownloadPressed,
             icon: Icon(