MINOR: Replace ConfiguredTopology with TopologyValidationResult

[lucasbru]

Summary

This refactoring simplifies the streams group coordinator by replacing
the ConfiguredTopology, ConfiguredSubtopology, and
ConfiguredInternalTopic classes with a simpler
TopologyValidationResult record.

TopologyValidationResult is a new record that captures the validation
state of a topology, including the topology epoch, internal topics to be
created, any configuration exceptions, and an optional
maxPartitionsPerSubtopology map when the topology is ready. Storing
only the pre-computed map (instead of TopologyMetadata) avoids
retaining a reference to CoordinatorMetadataImage in Timeline
collections.

TopologyMetadata is now a lightweight class that accepts pre-computed
partition counts and StreamsTopology. It is constructed on-the-fly in
TargetAssignmentBuilder when needed, rather than being stored in
TopologyValidationResult. The computeAllMaxPartitions method was
moved from TopologyMetadata to InternalTopicManager.

InternalTopicManager.configureTopics now returns
TopologyValidationResult with maxPartitionsPerSubtopology directly.
The topology metadata is only created when all required topics exist.

StreamsGroup stores TopologyValidationResult instead of
ConfiguredTopology, with renamed accessor methods.

TargetAssignmentBuilder now accepts both TopologyValidationResult
and StreamsTopology via withTopology(), and constructs
TopologyMetadata on the fly when the topology is ready.

EndpointToPartitionsManager now takes StreamsTopology directly as a
parameter instead of fetching it from StreamsGroup, which fixes a
timing issue during heartbeat processing.

The three Configured* classes and their tests are deleted as they are
no longer needed.

The jmh-benchmarks module has been updated to use the new
TopologyMetadata constructor with StreamsTopology and pre-computed
max partitions.

Test plan

• Unit tests pass: TopologyValidationResultTest,
  TopologyMetadataTest, InternalTopicManagerTest,
  TargetAssignmentBuilderTest, EndpointToPartitionsManagerTest,
  StreamsGroupTest
• All GroupMetadataManagerTest tests pass (410+ tests)
• All streams group coordinator tests pass
• Checkstyle and spotless checks pass
• JMH benchmarks compile and pass style checks