KIP-138 — Change punctuate semantics

Accepted Kafka 1.0 Streams

KIP-138 refactors the Kafka Streams `Punctuator` API to support two independent scheduling modes: `STREAM_TIME` (driven by record timestamps) and `WALL_CLOCK_TIME` (driven by system wall-clock time), each schedulable independently per processor. Previously `punctuate()` was triggered only by stream-time advance, so wall-clock-based periodic actions (e.g., flushing caches) stalled whenever any input partition stopped receiving records.

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