KIP-341 — Update Sticky Assignor's User Data Protocol

Accepted Kafka 2.3 Consumer

Updates the `StickyAssignor`'s user-data protocol to encode the previous assignment generation ID alongside the partition assignment, allowing the leader to detect and discard stale assignment reports from members that missed a generation. Without the generation ID, a consumer rejoining after a missed rebalance reports an outdated assignment, causing the sticky assignor's leader to start from a suboptimal partition distribution.

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