KIP-527 — Add VoidSerde to Serdes

Accepted Kafka 2.5 Streams

KIP-527 adds a `Serdes.Void()` serde to the Kafka Streams API that serializes/deserializes `Void` (always null), providing a type-safe representation of topics where keys or values are always null. Using `BytesSerde` or `ByteArraySerde` for null-keyed topics produces a misleading `KStream<Bytes, V>` type that requires defensive null checks throughout the topology.

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