[Backport dev/1.3] [Pipe] Fix tablet type conversion for failed columns

[Caideyipi]

Description

Backports #18595 (31e7534811217440172d3b2edd27170ef8328c19) to dev/1.3.

Pipe and Load conversion retries can restore failed measurements whose source type or value column is missing. Validate tablet column state before conversion so those measurements remain failed while valid columns still convert successfully.

The production changes apply unchanged. The regression tests use the 1.3 public validateMeasurementSchema entry point and TsFile API, and construct partial-insert failures through markFailedMeasurement.

Validation

• mvn spotless:apply -pl iotdb-core/datanode: passed.
• mvn test -pl iotdb-core/datanode -am -Dtest=PipeConvertedInsertTabletStatementTest -Dsurefire.failIfNoSpecifiedTests=false: passed, all 26 reactor modules successful and all 3 regression tests passing.
• Ran the same tests against the pre-backport converter classes: all 3 fail, reproducing out-of-bounds access in Pipe/Load and an incorrectly retained null-typed measurement.

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This PR has:

• been self-reviewed.
• added Javadocs for the non-trivial validation method.
• added unit tests covering Pipe and Load conversion of failed columns.

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Key changed/added classes

• PipeConvertedInsertTabletStatement
• LoadConvertedInsertTabletStatement
• PipeConvertedInsertTabletStatementTest