fix: account deletion: clear cache

[neooriginal]

This pull request makes a small but important improvement to the account deletion flow. After a user deletes their account and signs out, it now also clears all files managed by WalFileManager to ensure more thorough cleanup of user data.

• Account deletion flow:
  • Added a call to WalFileManager.clearAll() after signing out to clear all WAL-managed files.
  • Imported omi/utils/wal_file_manager.dart to support the new cleanup step.

[gemini-code-assist]

Code Review

This pull request adds a call to clear WalFileManager files during account deletion, which is a good improvement for data cleanup. However, I've identified a critical issue in the deleteAccountNow function related to error handling and an unawaited asynchronous call. An error during the deletion process could leave the app in an unresponsive state. The recommendation for a try-catch-finally block for error handling aligns with repository guidelines for operations with non-negligible failure chances. I've provided feedback on how to make this process more robust.

[beastoin]

lgtm @neooriginal