Subscription: clean up consumers after abrupt disconnect

[Caideyipi]

Summary

• retain disconnected subscription receivers until server-side inactivity cleanup completes
• serialize request, reconnect, exit, and timeout handling per consumer identity, fencing obsolete connections after reconnect
• keep timeout state retryable when consumer cleanup fails, and remove it after explicit close or successful timeout cleanup

Motivation

An abruptly terminated consumer does not send close or unsubscribe requests. The server previously removed its receiver from timeout tracking and cleared the receiver's shared consumer state during connection cleanup, so the orphaned consumer could retain uncommitted subscription data indefinitely. That retained data can exhaust shared subscription memory and block message admission for unrelated topics and consumers.

Tests

• mvn -o -nsu spotless:check -pl iotdb-core/datanode
• targeted Checkstyle for SubscriptionReceiver*.java (0 violations)
• SubscriptionReceiverAgentTest: 4 tests passed
• SubscriptionReceiverV1Test: 9 tests passed