feat(mobile): add bulk download functionality (#18878)

* feat(mobile): add bulk download functionality and update UI messages

- Added `downloadAll` method to `IDownloadRepository` and its implementation in `DownloadRepository` to handle multiple asset downloads.
- Implemented `downloadAllAsset` in `DownloadStateNotifier` to trigger bulk downloads.
- Updated `DownloadService` to create download tasks for all selected assets.
- Enhanced UI with new download success and failure messages in `en.json`.
- Added download button to `ControlBottomAppBar` and integrated download functionality in `MultiselectGrid`.

* translations use i18n method t()

* Update mobile/lib/services/download.service.dart

Co-authored-by: shenlong <139912620+shenlong-tanwen@users.noreply.github.com>

* fix(mobile): update download logic in DownloadService

- Changed the download method to utilize downloadAll for handling multiple tasks.
- Simplified remoteId check by removing unnecessary condition.

* sort i18n keys

* remove the download signature from interface and logic as we use the downloadAll now

---------

Co-authored-by: shenlong <139912620+shenlong-tanwen@users.noreply.github.com>

mobile/lib/models/asset_selection_state.dart

@@ -35,7 +35,7 @@ class AssetSelectionState {
 
   @override
   String toString() =>
-      'SelectionAssetState(hasRemote: $hasRemote, hasMerged: $hasMerged, hasMerged: $hasMerged, selectedCount: $selectedCount)';
+      'SelectionAssetState(hasRemote: $hasRemote, hasLocal: $hasLocal, hasMerged: $hasMerged, selectedCount: $selectedCount)';
 
   @override
   bool operator ==(covariant AssetSelectionState other) {