KIP-45 — Standardize all client sequence interaction on j.u.Collection.

Discussion Consumer

KIP-45 standardizes all `KafkaConsumer` API methods that accept or return collections to use `java.util.Collection` instead of `java.util.List` for inputs and vararg arrays for multi-partition methods (`pause`, `resume`, `seekToBeginning`, `seekToEnd`). The inconsistency—`subscribe()` takes a List but `subscription()` returns a Set, while pause/resume use varargs—creates friction and forces unnecessary copies when chaining API calls.

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