[KafkaIO] Use consumer position and lag to estimate end offsets in KafkaUnboundedReader

[sjvanrossum]

Use Consumer.position(TopicPartition) and Consumer.currentLag(TopicPartition) to update the latest offset in PartitionState.

This change reuses local metadata from recently completed record fetches instead of periodically requesting the broker for end offsets.

This PR is a follow up to #39285 with additional changes to reduce synchronization overhead in consumerPollLoop to a minimum since PartitionState will likely be updated more frequently than the offset consumer interval.

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[github-actions]

Reminder, please take a look at this pr: @kennknowles @johnjcasey

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Reminder, please take a look at this pr: @Abacn @kennknowles

[kennknowles]

R: @an2x

Since this is a followup to #39285 and thing you have context on.

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