Kafka Streams runner: committed metrics

The Kafka Streams runner reports only attempted metric values. `MetricResults` exposes what the SDK harness reported per bundle, folded into the job's step map, with no committed variant, and `UsesCommittedMetrics` is excluded from the ValidatesRunner suite.

Committed metrics would need the metric updates to be committed atomically with the records and offsets of the bundle that produced them.

Part of #18479.

Start by tracing MetricResults and the Kafka Streams runner's bundle handling, then inspect UsesCommittedMetrics and the ValidatesRunner suite. Determine how metric updates can be committed atomically with each bundle's records and offsets; done means committed metrics are exposed and the suite covers them.

Written by the indexing model from the issue text.