fix(client-v2): classify insert write failures as transfer errors

[014-code]

Summary

Closes #2729

This PR fixes exception classification for POJO inserts in client-v2.

Previously, Client.insert(...) could wrap request-body write failures such as
java.net.SocketException: Broken pipe (Write failed) into
DataSerializationException while serializing POJOs. That made transport failures
look like serialization bugs.

This change stops catching IOException inside the POJO field serialization loop,
so write-time network failures continue through the transport error path and are
reported as DataTransferException instead.

Actual POJO reflection/serialization failures are unchanged and still surface as
DataSerializationException.

Compatibility impact:
This is a bug fix with no public API signature change. The only user-visible behavior
change is the exception type reported for request-body transport failures during
Client.insert(...).

Tests:

• Added a regression test for a broken-pipe style write failure during POJO insert
• Added a regression test to preserve DataSerializationException for real getter failures

Local verification:

• mvn -pl client-v2 -am -DskipITs=true -Dtest=InsertExceptionClassificationTest -Dsurefire.failIfNoSpecifiedTests=false test

Checklist

• Closes DataSerializationException caused by java.net.SocketException: Broken pipe (Write failed) #2729
• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG
• For significant changes, documentation in https://github.com/ClickHouse/clickhouse-docs was updated with further explanations or tutorials

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[chernser]

@014-code Thank you for the contribution!