[To dev/1.3] [Pipe] Fix pipe sink metrics lifecycle race (#18722)

[Caideyipi]

Description

Backport of #18722 (commit ce6c1f5f477b2da5b5071890c715c6b6a9652e45) to dev/1.3.

PipeDataRegionSinkMetrics now serializes bindTo, unbindFrom, register, and deregister so a sink task remains present throughout metric creation and removal. This prevents concurrent deregistration from causing a null pointer exception while metrics are being bound during DataNode startup.

The source conflict was adapted to the dev/1.3 connector naming and API; the regression test uses the branch's existing getConnectorIndex() method.

Verification

• .\mvnw.cmd --% -pl iotdb-core/datanode spotless:apply -Ddevelocity.off=true
• .\mvnw.cmd --% -pl iotdb-core/datanode -Dtest=PipeDataRegionSinkMetricsTest test -Ddevelocity.off=true
• Build succeeded; the targeted test passed in both configured Surefire executions with 0 failures and 0 errors.

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This PR has:

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

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Key changed/added classes in this PR

• PipeDataRegionSinkMetrics
• PipeDataRegionSinkMetricsTest