Load balance service patch

[CRZbulabula]

1. For ClusterPartitionFetcher, we should remove the duplicated consensus group ids before fetching schema partitions.
2. The previous statistics maps should be cleaned when the corresponding ConfigNode is no longer the leader; otherwise the ConfigNode would take obsolete statistics when next time it becomes the leader.

[Copilot]

Pull request overview

This PR improves load-balancing and partition-fetching correctness in IoTDB’s cluster mode by reducing redundant region-route lookups and preventing stale load statistics from being reused across ConfigNode leadership changes.

Changes:

• Deduplicate consensus group IDs when resolving schema partitions in ClusterPartitionFetcher.
• Clear previously recorded node/region/consensus statistics when stopping EventService (e.g., on leadership change).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/analyze/ClusterPartitionFetcher.java	Attempts to deduplicate schema consensus group IDs before fetching replica sets.
iotdb-core/confignode/src/main/java/org/apache/iotdb/confignode/manager/load/service/EventService.java	Clears cached “previous” statistics maps on event service stop to avoid stale state after leadership changes.

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 0% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 39.82%. Comparing base (1c1cbca) to head (52d42aa).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
...ryengine/plan/analyze/ClusterPartitionFetcher.java	0.00%	6 Missing ⚠️
.../confignode/manager/load/service/EventService.java	0.00%	5 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## master #17463 +/- ##
============================================
- Coverage 39.82% 39.82% -0.01% 
Complexity 312 312 ============================================
Files 5135 5135 Lines 347073 347083 +10 Branches 44220 44222 +2 ============================================
- Hits 138221 138215 -6 - Misses 208852 208868 +16 

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