KIP-794 — Strictly Uniform Sticky Partitioner

Accepted Kafka 3.3 Producer

Replaces the `UniformStickyPartitioner` with a strictly uniform variant that switches the target partition based on the number of records sent rather than on batch creation events. The original sticky partitioner sent disproportionately more records to slower brokers because batches were created more frequently for them, creating a positive-feedback loop that worsened the slowdown.

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