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>

i18n/en.json

@@ -463,6 +463,8 @@
   "assets_count": "{count, plural, one {# asset} other {# assets}}",
   "assets_deleted_permanently": "{count} asset(s) deleted permanently",
   "assets_deleted_permanently_from_server": "{count} asset(s) deleted permanently from the Immich server",
+  "assets_downloaded_failed": "{count, plural, one {Downloaded # file - {error} file failed} other {Downloaded # files - {error} files failed}}",
+  "assets_downloaded_successfully": "{count, plural, one {Downloaded # file successfully} other {Downloaded # files successfully}}",
   "assets_moved_to_trash_count": "Moved {count, plural, one {# asset} other {# assets}} to trash",
   "assets_permanently_deleted_count": "Permanently deleted {count, plural, one {# asset} other {# assets}}",
   "assets_removed_count": "Removed {count, plural, one {# asset} other {# assets}}",
@@ -1170,7 +1172,7 @@
   "look": "Look",
   "loop_videos": "Loop videos",
   "loop_videos_description": "Enable to automatically loop a video in the detail viewer.",
-  "main_branch_warning": "You’re using a development version; we strongly recommend using a release version!",
+  "main_branch_warning": "You're using a development version; we strongly recommend using a release version!",
   "main_menu": "Main menu",
   "make": "Make",
   "manage_shared_links": "Manage shared links",
@@ -1435,7 +1437,7 @@
   "purchase_lifetime_description": "Lifetime purchase",
   "purchase_option_title": "PURCHASE OPTIONS",
   "purchase_panel_info_1": "Building Immich takes a lot of time and effort, and we have full-time engineers working on it to make it as good as we possibly can. Our mission is for open-source software and ethical business practices to become a sustainable income source for developers and to create a privacy-respecting ecosystem with real alternatives to exploitative cloud services.",
-  "purchase_panel_info_2": "As we’re committed not to add paywalls, this purchase will not grant you any additional features in Immich. We rely on users like you to support Immich’s ongoing development.",
+  "purchase_panel_info_2": "As we're committed not to add paywalls, this purchase will not grant you any additional features in Immich. We rely on users like you to support Immich's ongoing development.",
   "purchase_panel_title": "Support the project",
   "purchase_per_server": "Per server",
   "purchase_per_user": "Per user",