STORM-4041: fix(topology_lag): Kafka Topology Lag breaking when no offsets are committed (Backport #8589)

[reiabreu]

What is the purpose of the change

This is a backport of #8589 to the 2.x branch.

It fixes a regression where the Kafka spout lag reporting in the Storm UI would fail silently (throwing a ClassCastException in logs) when partitions had no committed offsets.

Brief change log

• KafkaOffsetLagUtil: Optimized offset retrieval using batch calls and added null-checks to handle partitions without committed offsets (reporting -1 instead of crashing).
• TopologySpoutLag: Improved JSON parsing logic to safely handle non-JSON error messages from the monitor subprocess, preventing ClassCastException.
• Integration Test: Added KafkaOffsetLagUtilTest using Testcontainers to verify the fix.

Related Issues

• Original Issue: STORM-4041
• Original PR: fix(topology_lag): Kafka Topology Lag breaking when no offsets are commited for topic/partition #8589

Verifying this change

• Added KafkaOffsetLagUtilTest which passes locally on the 2.x branch.
• Manually verified compilation of storm-kafka-monitor.