Reconsider page server logging for offline validation.

In the linked validation log, I observed 14,548 of the 20,489 lines (71%) were one repeated warning (logid: 13067400):

"No candidate page server is known to have materialized the requested LSN, continuing with existing routing"

Another warning, (logid: 13295600) "ClosedSegmentCompletionTracker: materialization frontier has not advanced", fires once a minute per cell for the whole run with frontier: "none". StalledMillis begins at a minute and builds to a few hours by the end of the multi-hour validation run.

Why I think it may be safe to suppress in this mode specifically.

Every instance reports knownFrontierCount: 0 and maxKnownFrontier: null. So it reads less like "the page servers are behind" and more like "this node never learned what they've materialized." That seems expected here: an offline validation node is pinned to a checkpoint and doesn't tail the log, so the path that normally populates the frontier (notifyMaterializationFrontierUpdated, reached from LogServerManager::_notifyMaterializationUpdate when materialized offsets arrive from log servers) never runs. If that's right, the condition being warned about can't be satisfied in this mode at all, rather than indicating something wrong.