release-23.2: streamingccl: only return lag replanning error if lagging node has not advanced

[blathers-crl]

Backport 1/1 commits from #115000 on behalf of @msbutler.

/cc @cockroachdb/release

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Previously, the frontier processor would return a lag replanning error if it detected a lagging node and after the hwm had advanced during the flow. This implies the frontier processor could replan as soon as a lagging node finished its catchup scan and bumped the hwm, but was still far behind the other nodes, as we observed in #114706. Ideally, the frontier processor should not throw this replanning error because the lagging node is making progress and because replanning can cause repeated work.

This patch prevents this scenario by teaching the frontier processor to only throw a replanning error if:

• the hwm has advanced in the flow
• two consecutive lagging node checks detected a lagging node and the hwm has not advanced during those two checks.

Informs #114706

Release note: none

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Release justification: low risk, c2c only, bug fix

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

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[cockroach-teamcity]

This change is