fix(mobile): get provider refs before async gaps in backup page

[LeLunZ]

Description

I actually had this in my logs now way to often, finally took the time to look into what's failing.

In the backup page we wait on the getBackupStatus/syncRemote if a user closes the page when its still loading we get this error afterwards:

Bad state: Cannot use "ref" after the widget was disposed.
#0      ConsumerStatefulElement._assertNotDisposed (package:flutter_riverpod/src/consumer.dart:550)
#1      ConsumerStatefulElement.read (package:flutter_riverpod/src/consumer.dart:619)
#2      _DriftBackupPageState.initState.<anonymous closure> (package:immich_mobile/pages/backup/drift_backup.page.dart:52)
<asynchronous suspension>

To fix the issue, I read the providers at the beginning of the function so we can still call backupNotifier.updateSyncing after the widget has been disposed.

How Has This Been Tested?

• manual ui test

Checklist:

• I have carefully read CONTRIBUTING.md
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if applicable
• I have no unrelated changes in the PR.
• I have confirmed that any new dependencies are strictly necessary.
• I have written tests for new code (if applicable)
• I have followed naming conventions/patterns in the surrounding code
• All code in src/services/ uses repositories implementations for database calls, filesystem operations, etc.
• All code in src/repositories/ is pretty basic/simple and does not have any immich specific logic (that belongs in src/services/)

Please describe to which degree, if any, an LLM was used in creating this pull request.

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[LeLunZ]

@alextran1502 sorry I just noticed the issue also occurs in the startBackup function and added a commit to fix it