Remove inflightResponses in server when connection is inactive.

### Search before asking

- [x] I searched in the [issues](https://github.com/alibaba/fluss/issues) and found nothing similar.

### Motivation

In Kafka, if the connection is inactive in server , it will remove inflightResponses kafka.network.Processor#processDisconnected:
```java

private def processDisconnected(): Unit = {
selector.disconnected.keySet.forEach { connectionId =>
try {
val remoteHost = ConnectionId.fromString(connectionId).getOrElse {
throw new IllegalStateException(s"connectionId has unexpected format: $connectionId")
}.remoteHost
inflightResponses.remove(connectionId).foreach(updateRequestMetrics)
// the channel has been closed by the selector but the quotas still need to be updated
connectionQuotas.dec(listenerName, InetAddress.getByName(remoteHost))
} catch {
case e: Throwable => processException(s"Exception while processing disconnection of $connectionId", e)
}
}

```
Same thing can also do in fluss.

### Solution

_No response_

### Anything else?

_No response_

### Willingness to contribute

- [ ] I'm willing to submit a PR!

Start by locating Fluss's server connection-disconnection handling and the inflightResponses state, then compare it with the referenced Kafka entry point, kafka.network.Processor#processDisconnected. Confirm the expected cleanup when a connection becomes inactive and identify the relevant server tests or add coverage showing that the stale response state is removed.

Written by the indexing model from the issue text.