KIP-773 — Differentiate consistently metric latency measured in millis and nanos

Accepted Kafka 3.1 MetricsProducer

Renames the producer metrics `bufferpool-wait-time-total`, `io-waittime-total`, and `iotime-total` to include `-ns` or `-ms` suffixes (e.g., `bufferpool-wait-time-ns-total`) to make the unit explicit and consistent with the rest of the metric family. These three metrics deviate from the established naming convention where nanosecond metrics include `-ns` in their name, causing confusion about units.

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