Regularly check for `PreviousStepStillProcessingError` cache entries
`PreviousStepStillProcessingError` errors should be transient cache entries. If they exist for longer than... days, we should consider them obsolete and refresh their ancestors, or, simpler: the whole dataset.

Regularly check for `PreviousStepStillProcessingError` cache entries: `PreviousStepStillProcessingError` errors should be transient cache entries. If they exist for longer than... days, we should consider them obsolete and refresh their ancestors, or, simpler: the whole dataset.
