Upgrade kafka-clients to 4.2.0 and fix deprecated API usage

[pjfanning]

Summary

Upgrades kafka-clients from 4.1.2 to 4.2.0 and fixes all compilation issues caused by newly deprecated/removed APIs.

Changes

Version bump

• kafkaVersion = "4.1.2" → "4.2.0" in project/Versions.scala

ConsumerGroupMetadata constructors (deprecated with forRemoval=true in 4.2.0)

Instead of creating new ConsumerGroupMetadata(groupId) in TransactionalProducerStage, the actual ConsumerGroupMetadata is now threaded from the Kafka consumer through the message pipeline:

• Added groupMetadata: Option[ConsumerGroupMetadata] to KafkaConsumerActor.Internal.Messages
• KafkaConsumerActor includes consumer.groupMetadata() when sending non-empty messages
• Added onGroupMetadata hook to BaseSingleSourceLogic and SubSourceLogic
• Added consumerGroupMetadata: ConsumerGroupMetadata abstract method to TransactionalMessageBuilderBase
• TransactionalSourceLogic and TransactionalSubSourceStageLogic track the current group metadata
• Added consumerGroupMetadata field to PartitionOffsetCommittedMarker
• TransactionalProducerStage.commitTransaction now uses batch.groupMetadata directly

This is a proper fix (not just suppression): transactions now use the actual consumer's group metadata (including generation ID and member ID), which provides proper zombie-fencing semantics for EOS.

consumer.close(Duration) (deprecated)

Replaced with consumer.close(CloseOptions.timeout(duration)) in KafkaConsumerActor.postStop; removed now-unneeded @nowarn annotation.

ConsumerGroupDescription.state() / ConsumerGroupState (deprecated since 4.0, forRemoval=true)

Replaced with groupState() / GroupState.STABLE in both KafkaSpec.scala and BaseKafkaTest.java.

Benchmark

Replaced new ConsumerGroupMetadata(fixture.groupId) with consumer.groupMetadata() (the fixture has a real KafkaConsumer reference).

Test infrastructure

ConsumerDummy.groupMetadata() now returns a non-throwing stub value. A @nowarn("msg=deprecated") annotation is used here since it's a mock consumer without a real Kafka connection, making the deprecated constructor the only option in this context.