emqx4.3/changes/ce/fix-13072.en.md

Various fixes related to the durable_sessions feature:

• Add an option to execute read operations on the leader.
• drop_generation operation can be replayed multiple times by the replication layer, but it's not idempotent. This PR adds a workaround that avoids a crash when drop_generation doesn't succeed. In the future, however, we want to make drop_generation idempotent in a nicer way.
• Wrap storage layer events in a small structure containing the generation ID, to make sure events are handled by the same layout CBM & context that produced them.
• Fix crash when storage event arrives to the dropped generation (now removed storage_layer:generation_at function didn't handle the case of dropped generations).
• Implement format_status callback for several workers to minimize log spam
• Move the responsibility of end_of_stream detection to the layout CBM. Previously storage layer used a heuristic: old generations that return an empty batch won't produce more data. This was, obviously, incorrect: for example, bitfield-LTS layout MAY return empty batch while waiting for safe cutoff time.
• reference layout has been enabled in prod build. It could be useful for integration testing.
• Fix incorrect epoch calculation in bitfield_lts:handle_event callback that lead to missed safe cutoff time updates, and effectively, subscribers being unable to fetch messages until a fresh batch was published.