KIP-33 — Add a time based log index

Accepted Kafka 1.0 Broker

Adds a time-based index (.timeindex file) per log segment that maps message timestamps to file offsets, enabling accurate offset-by-timestamp lookups (ListOffsets by timestamp) and time-based log rolling/retention at per-message-timestamp granularity. The previous implementation relied on file modification times for time-based operations, which broke on replica reassignment and provided only segment-level (coarse) timestamp resolution.

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