[Subscription] Skip runtime when subscription is disabled

[Caideyipi]

Description

When subscription_enabled=false, avoid initializing or running DataNode subscription runtime components:

• Skip registration of the Subscription Runtime Agent service.
• Do not schedule the subscription receiver timeout checker.
• Return successful no-op responses for subscription progress/runtime RPCs.
• Keep updating the normal region cache while skipping subscription route callbacks.
• Avoid accessing the subscription receiver on ordinary client disconnects.
• Defensively ignore runtime-state updates in ConsensusSubscriptionSetupHandler.

This removes the misleading runtime-service startup log, the SubscriptionReceiverAgent-Timeout-Checker thread, and subscription runtime-state logs while subscription is disabled.

Tests

• mvn -o -nsu validate -pl iotdb-core/datanode
• mvn -nsu -pl iotdb-core/datanode -am test -Dtest=SubscriptionReceiverAgentTest,ConsensusSubscriptionSetupHandlerTest,DataNodeInternalRPCServiceImplSubscriptionDisabledTest -Dsurefire.failIfNoSpecifiedTests=false -DfailIfNoTests=false
  • 12 tests passed in a clean worktree.

---

This PR has:

• been self-reviewed.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage.

---

Key changed/added classes (or packages if there are too many classes) in this PR

• DataNode
• ClientRPCServiceImpl
• DataNodeInternalRPCServiceImpl
• SubscriptionReceiverAgent
• ConsensusSubscriptionSetupHandler