databendlabs / openraft / 20272458143

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refactor: add `StreamId` for unique replication stream identification

This change introduces `StreamId` and `SharedIdGenerator` to uniquely identify
replication streams, replacing the previous session-based identification.
Adds `CloseReplicationStreams` command variant for when there are no replication
targets, and adds `leader_vote` field to `RebuildReplicationStreams` and
`ReplicateSnapshot` commands for proper leader identification.

Why:

Before this commit, we used a replication session ID to determine if a
notification message is valid. With this approach, when the membership changes
(e.g., a new membership is appended to the local log), the replication session
ID changes, causing all ongoing replication notifications to be considered
invalid.

This approach is too aggressive - it invalidates notifications that are actually
still valid. For example, if the membership changes from {1,2,3} to {1,2,3,4},
ongoing replication to node 2 or node 3 is still valid because these nodes
remain unchanged in the new membership. But before this commit, these
notifications were simply discarded.

This resulted in fake message loss: valid notification messages were discarded,
causing some tests to fail spuriously.

With this commit, we switch to a new approach: instead of using leader vote and
membership ID to identify notification validity, we assign a unique `StreamId`
to each replication stream. For example, replication to node 2 has a unique
stream ID. As long as this node is present in the membership configuration, the
stream ID remains valid. With this new approach, notification messages won't be
discarded even during membership changes, eliminating the spurious test
failures.

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