KIP-1064 — Upgrade slf4j to 2.x

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Upgrades Kafka's logging interface from SLF4J 1.7 to SLF4J 2.0 and updates the default log4j2 binding to log4j-slf4j2-impl, enabling the -Dslf4j.provider JVM property for logging backend selection. SLF4J 1.x required classpath ordering tricks or manual JAR removal to select a logging backend, and Kafka's dependency on it prevented users from easily switching to modern logging implementations.

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