fix(inkless): allow searching offsets in UnifiedLog only if switched topics are in sync

[giuseppelillo]

Allow OffsetsForLeaderEpoch to be handled by replicas in case they have replicated up to classicToDisklessOffset.
Add the same check for ListOffsets, which previously always allowed requests to be handled by every follower.

[Copilot]

Pull request overview

This PR tightens classic-path offset lookup behavior for diskless “hybrid/switched” partitions so that followers only serve classic-side ListOffsets / OffsetsForLeaderEpoch when they have fully caught up to the committed classicToDisklessStartOffset (the sealed classic prefix boundary).

Changes:

• Gate classic-path follower handling for ListOffsets on whether the local log’s HW has reached the committed switch offset.
• Allow OffsetsForLeaderEpoch to be answered by non-leader replicas only when they have the complete sealed classic prefix locally.
• Add/extend unit tests covering the boundary cases for both routing (ListOffsets) and leader-epoch lookups.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
core/src/main/scala/kafka/server/ReplicaManager.scala	Passes a “complete classic prefix” predicate into DisklessFetchOffsetRouter and relaxes OffsetsForLeaderEpoch leader-only behavior only when the local sealed prefix is complete.
core/src/main/scala/kafka/server/DisklessFetchOffsetRouter.scala	Adds follower-eligibility gating based on completeness of the sealed classic prefix when routing ListOffsets on switched/hybrid partitions.
core/src/test/scala/unit/kafka/server/ReplicaManagerTest.scala	Adds tests asserting follower behavior at the switch boundary for lastOffsetForLeaderEpoch (allowed when caught up; rejected when lagging).
core/src/test/scala/unit/kafka/server/DisklessFetchOffsetRouterTest.scala	Adds tests ensuring switched/hybrid follower access is denied when the classic prefix is incomplete (including consolidating + committed-boundary scenarios).

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