Update Java to 21 and Kafka + Hazelcast to latest versions#4

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SoerenHenning wants to merge 2 commits intomainfrom

upgrade-java-kstreams-hzcast

Commits on Apr 20, 2026

Update build configurations and dependencies to use Java 21 and latest Kafka clients, Kafka Streams and Hazelcast
SoerenHenning
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Commits on Apr 21, 2026

Merge branch 'main' into upgrade-java-kstreams-hzcast
SoerenHenning
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