Remove potential ID collision in ECA cron events

Problem/Motivation

This is a follow-up on 🐛 Multiple cron events not firing consistently Fixed and there are 2 MRs which can be reviewed and tested as a feature request here as the other issue was a bug report that's fixed under given circumstances.

The cron events come with an ID and store a state key derived from that ID which holds the last execution time.

The IDs are not guaranteed to be unique. This doesn't matter at this point, as cron runs only once per PHP request. However, if that should ever change, the IDs need to be unique.

Proposed resolution

Test and review the MRs attached to the related issue.

In addition to that, we need to consider a way on how to clean-up state keys that are no longer required.