feat: load account should return db error

[yjhmelody]

Since the db may be a remote db, it could happen a network error under the db error.
And when remote db error happen, the application level maybe need to retry it. So it's better to keep db error original rather than be a custom string.

Or just return another db error with extra error info?

[rakita]

seems resonable.
cc @refcell

[rakita]

failed tests not related