Implement LogManager for TransactionManager

Implement the LogManager interface for TransactionManager, allowing it to notify LogConsumers of new log entries and prune entries when all consumers have processed them. The manager stores the last acknowledged LSN for each consumer, but does not retain this state across restarts. On restart, the oldest LSN present will be treated as the low water mark for consumers. If a consumer has already processed that LSN, its next acknowledgement will inform the manager of its actual position.

To avoid injecting acknowledgements into the entire TransactionManager test suite, we only add a LogConsumer to the new consumer-related tests.