GetGroupLag is similar to `kadm.Client.Lag` but works when the group doesn't have live participants.

mimics `NewReader` constructor but builds a reader service using a reader.

KafkaReader provides low-level access to Kafka partition reading operations.

Partition level metadata in a more easily digestible form than what Kafka provides.

ReaderMetrics contains metrics specific to Kafka reading operations.

Committer defines an interface for committing offsets.