MINOR: Move TransactionStateManager leaf case classes to Java records in transaction-coordinator

[sjhajharia]

Summary

As part of the larger effort to move TransactionStateManager from core
to the transaction-coordinator module and convert it to Java, this PR
extracts the 7 leaf data classes that lived inside
TransactionStateManager.scala and reimplements them as Java records in
org.apache.kafka.coordinator.transaction. They have no coupling to the
manager itself and can move independently.

Changes

New Java records in transaction-coordinator:

• TransactionPartitionAndLeaderEpoch
• TransactionalIdAndProducerIdEpoch : custom toString preserved (used in
  log messages)
• CoordinatorEpochAndTxnMetadata
• TransactionalIdCoordinatorEpochAndMetadata
• TransactionalIdCoordinatorEpochAndTransitMetadata
• TxnMetadataCacheEntry : custom toString preserved (coordinatorEpoch=X,
  numTransactionalEntries=Y)
• TransactionConfig : declares a no-arg constructor that delegates to
  the canonical 11-arg constructor with the same *_DEFAULT constants the
  old Scala defaults referenced, preserving the TransactionConfig() test
  ergonomics

Removed from TransactionStateManager.scala: all 7 case class
definitions; unused ServerConfigs import.

Call-site updates:

• TransactionStateManager.scala, TransactionCoordinator.scala : added
  imports, prepended new to record construction.
• 5 test files: TransactionStateManagerTest, TransactionCoordinatorTest,
  TransactionCoordinatorConcurrencyTest,
  TransactionMarkerRequestCompletionHandlerTest,
  TransactionMarkerChannelManagerTest : same treatment.