[Subscription] Fix consensus subscription metrics across Regions

[Caideyipi]

Description

Isolate consensus subscription metrics by Region

Consensus subscription queues from different Regions can share the same consumer-group/topic queue ID. The metrics singleton previously keyed queues and rates only by that ID, so one Region overwrote or hid the others.

This change keys metric state by (queue ID, Region ID), adds the region tag to every consensus-subscription metric, passes the Region when marking transfer rates, and removes only the matching Region's gauges and rate. Metric lifecycle operations are serialized and stale queue instances cannot deregister the active instance for the same key.

Make catch-up status observable and accurate

• Add subscription_consensus_active, subscription_consensus_initialized, and subscription_consensus_seek_generation.
• Keep subscription_current_commit_id for dashboard compatibility while exposing its actual seek-generation meaning under the new metric name.
• Include entries waiting in the linger batch in subscription_consensus_lag, so lag cannot report zero while accepted data is still waiting to be emitted.
• Remove stale per-Region Rate objects during deregistration.

For a stopped workload, an initialized active Region with zero lag now means the queue has no buffered, in-flight, pending, lingered, or unread WAL work.

Verification

• mvn -Ddevelocity.off=true spotless:apply -pl iotdb-core/node-commons,iotdb-core/datanode
• mvn -Ddevelocity.off=true checkstyle:check -pl iotdb-core/node-commons,iotdb-core/datanode
• Targeted unit tests: 12 tests, 0 failures/errors
  • ConsensusSubscriptionPrefetchingQueueMetricsTest
  • ConsensusPrefetchingQueueTest
• English and Chinese full-reactor test-compile were attempted. Both stop before the changed modules because generated iotdb-thrift-commons/.../TaskType.java cannot resolve javax.annotation in the local environment.

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This PR has:

• been self-reviewed.
  • concurrent read
  • concurrent write
  • concurrent read and write
• added comments explaining the why and the intent of the code wherever it would not be obvious.
• added unit tests or modified existing tests to cover new code paths.

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

• ConsensusSubscriptionPrefetchingQueueMetrics
• ConsensusPrefetchingQueue
• SubscriptionReceiverV1
• Metric