Revise violation index in check mode

[schillic]

Follow-up of #473.
We currently return the index of a violation in the continuous-post algorithm.
However, in the hybrid setting, after the first jump, the index will start from 1 again. So instead, we should also add the previous time steps.

Actually, returning an index is not very general, as this relies on a fixed time step for the whole analysis. I suggest that we instead return a time interval. This would also simplify the refactoring for the above approach, as it would not depend on the time step anymore: if the continuous-post algorithm returns a time interval, this can just be added to the time interval of when the analysis was triggered from the hybrid loop.