KIP-1002 — Fetch remote segment indexes at once

Discussion Tiered Storage

Adds a `RemoteStorageManager.fetchLogSegmentData(metadata, indexes)` batch API to retrieve all segment indexes (offset, time, transaction, leader epoch) in a single remote storage call alongside the log data. Currently each index type is fetched with a separate `fetchIndex()` call, multiplying remote storage round-trips per consumer fetch.

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