change: ETCM-12423 decouple block participation from slots

[AmbientTea]

Description

Removes dependency on slots and abstracts them into a Moment type

Checklist

• Commit sequence broadly makes sense and commits have useful messages.
• The size limit of 400 LOC isn't needlessly exceeded
• The PR refers to a JIRA ticket (if one exists)
• New tests are added if needed and existing tests are updated.
• New code is documented and existing documentation is updated.
• Relevant logging and metrics added
• Any changes are noted in the changelog.md for affected crate
• Self-reviewed the diff

[LGLO]

Generic Moment is better than a Slot, but using other Slot again as concrete type of Moment is a somehow lost opportunity here. The problem is that we still try to anchor some notion of timestamp.

The problem manifests in the most visible way when blockchain stopped to operate for some time and it is coming back. Then the wall-clock time of the block creation does not matter. We need at least on block per each past PC epoch to be created. It is created by a member of committee selected using SPDD from some past MC epoch (I mean, older than two epoch boundaries).

Not a deal breaker for me (we were happy with slots), but something to consider.

[AmbientTea]

Generic Moment is better than a Slot, but using other Slot again as concrete type of Moment is a somehow lost opportunity here. The problem is that we still try to anchor some notion of timestamp.

The problem manifests in the most visible way when blockchain stopped to operate for some time and it is coming back. Then the wall-clock time of the block creation does not matter. We need at least on block per each past PC epoch to be created. It is created by a member of committee selected using SPDD from some past MC epoch (I mean, older than two epoch boundaries).

Not a deal breaker for me (we were happy with slots), but something to consider.

Good catch, this is important, but we will address it as a separate issue.