[KAFKA-16191] Clean up of consumer client internal events

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 3.7.0
• Fix Version/s: 3.8.0
• Component/s: clients, consumer
• Labels: consumer-threading-refactor
• Assignee: Kirk True
• Reporter: Kirk True
• Reviewer: Bruno Cadonna
• Created: 24/Jan/24 18:14
• Updated: 29/Feb/24 10:24
• Resolved: 29/Feb/24 10:24

Description

There are a few minor issues with the event sub-classes in the 
org.apache.kafka.clients.consumer.internals package that should be cleaned up:

1. Update the names of subclasses to remove "Application" or "Background"
2. Make toString() final in the base classes and clean up the implementations of toStringBase()
3. Fix minor whitespace inconsistencies

Issue Links

• blocks: KAFKA-16100 Add timeout to all the CompletableApplicationEvents
• links to: GitHub Pull Request #15438