Stop evaluations that take too long

[fricklerhandwerk]

Since #405, starting the worker service will stop all ongoing evaluations (or mark stuck ones) by labeling them as crashed. We want to do this periodically in case evaluations go on longer than some reasonable time, such as 24h since that's our update period.

Implementation note:

add a supervisor timer unit that will check if there's any evaluation taking far too long (> 24 hours) and will forcibly restart the worker.
#405 (comment)