KIP-726 — Make the "cooperative-sticky, range" as the default assignor

Accepted Consumer

Changes the default `partition.assignment.strategy` for consumer groups from `RangeAssignor` to `[CooperativeStickyAssignor, RangeAssignor]` in Kafka 3.0, enabling incremental cooperative rebalancing by default. `RangeAssignor` uses eager (stop-the-world) rebalancing and can produce heavily skewed assignments when consumers subscribe to different topic sets, while `CooperativeStickyAssignor` avoids unnecessary partition revocation.

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