Stashing & Engine: EBM should only get triggered when there's a connection problem.

[khsrali]

Following this comment: https://github.com/aiidateam/aiida-core/pull/6746#discussion_r1982780386

And as the title says, we may silent EBM (Exponential Backoff Mechanism) for any errors un-related to transport issues.

To be investigated, if this is only towards stashing or, the entire engine (execmanager.py) should be revised for such errors.

[khsrali]

I removed the parent issue, because this is not only related to stashing.