Pipe: serialize sink transfers by region

[Caideyipi]

Description

This PR adds an optional Pipe sink config to serialize transfers within the same data region while keeping different data regions independently parallel.

• Add connector.serialize-by-region / sink.serialize-by-region, defaulting to true.
• When enabled, data region sink subtasks are grouped by region and use one sink subtask per region, so the same region is sent serially while different regions can still run in parallel.
• When sink/connector is not explicitly declared and serialize-by-region is enabled, default the IoTDB thrift sink to iotdb-thrift-sync-connector.
• Preserve explicit sink selection: iotdb-thrift-connector and iotdb-thrift-async-connector still use the async data-region sink.
• Preserve old connector.parallel.tasks / sink.parallel.tasks behavior when serialize-by-region=false.
• Remove the async sink in-flight handler waiting changes from this PR.

Tests

• git diff --check
• git diff --cached --check
• git diff origin/master -- iotdb-core/datanode/src/main/java/org/apache/iotdb/db/pipe/sink/protocol/thrift/async/IoTDBDataRegionAsyncSink.java
• mvn -DskipTests spotless:apply -pl iotdb-core/node-commons,iotdb-core/datanode
• mvn -DskipTests spotless:apply -pl integration-test -P with-integration-tests
• Attempted mvn -pl iotdb-core/datanode -Dtest=PipeDataNodePluginAgentTest test -Ddevelocity.off=true, but it is blocked before running tests by existing datanode compile errors in generated/queryengine/subscription sources, including missing parser contexts, missing IFill/IFillFilter, missing ComparatorChain, missing PERCENTILE, missing getModeMapSizeThreshold, TopicMeta owner methods, and a DataNodeTableOperatorGenerator#buildAggregator signature mismatch.

[codecov]

Codecov Report

❌ Patch coverage is 29.62963% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 40.93%. Comparing base (c39061a) to head (dc0e1a5).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
...gent/task/subtask/sink/PipeSinkSubtaskManager.java	0.00%	19 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #17946      +/-   ##
============================================
- Coverage     41.05%   40.93%   -0.12%     
  Complexity      318      318              
============================================
  Files          5258     5258              
  Lines        365541   365550       +9     
  Branches      47256    47259       +3     
============================================
- Hits         150081   149654     -427     
- Misses       215460   215896     +436     

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[sonarqubecloud]

Quality Gate passed

Issues
3 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