Wait for consensus start before answering region requests

[jt2594838]

Summary

• Add a lightweight polling utility (Await / ConditionAwaiter) in node-commons that provides a fluent API for waiting until a condition becomes true, with configurable timeout and poll interval.
• Introduce DataNodeContext inner class in DataNode to expose consensus initialization state (isAllConsensusStarted()), with volatile visibility on the underlying flags.
• Guard all region management RPCs in DataNodeInternalRPCServiceImpl (create/delete region, change leader, add/remove/delete/reset peer, notify migration) with a waitForConsensusStarted() check that polls up to 30 seconds before rejecting with CONSENSUS_NOT_INITIALIZED.
• This prevents race conditions where ConfigNode dispatches region requests to a DataNode whose consensus layer hasn't finished initializing after restart.

Test plan

• Unit tests for Await / ConditionAwaiter covering: already-true condition, condition becomes true, timeout, poll delay, exception ignoring, untilAsserted, forever mode (AwaitTest)
• Unit tests for consensus wait behavior: createSchemaRegion, createDataRegion, deleteRegion, changeRegionLeader all reject with CONSENSUS_NOT_INITIALIZED when consensus is not started (ConsensusWaitTest)
• Existing DataNodeInternalRPCServiceImplTest updated to pass a mocked DataNodeContext with consensus started

[codecov]

Codecov Report

❌ Patch coverage is 70.45455% with 39 lines in your changes missing coverage. Please review.
✅ Project coverage is 39.82%. Comparing base (acaabb8) to head (51b6674).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
...ol/thrift/impl/DataNodeInternalRPCServiceImpl.java	55.31%	21 Missing ⚠️
...che/iotdb/commons/concurrent/ConditionAwaiter.java	86.56%	9 Missing ⚠️
...e/iotdb/db/service/DataNodeInternalRPCService.java	0.00%	5 Missing ⚠️
...ain/java/org/apache/iotdb/db/service/DataNode.java	50.00%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #17546      +/-   ##
============================================
+ Coverage     39.80%   39.82%   +0.01%     
  Complexity      312      312              
============================================
  Files          5142     5147       +5     
  Lines        347882   348088     +206     
  Branches      44404    44430      +26     
============================================
+ Hits         138489   138618     +129     
- Misses       209393   209470      +77     

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[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
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