[VL][Delta] Add UniForm Iceberg support for Delta tables

[malinjawi]

Summary

Add UniForm Iceberg support for Delta tables on the Velox backend.

Today Gluten documents Iceberg readers (UniForm) as Not tested in docs/get-started/VeloxDelta.md. This issue tracks enabling and validating the supported Velox path.

Current state

Gluten already has some relevant hooks:

• backends-velox/src-delta33/main/scala/org/apache/spark/sql/delta/GlutenOptimisticTransaction.scala
  • materializes partition columns for Iceberg compat
  • tags AddFile entries with Iceberg compat version
• backends-velox/src-delta33/main/scala/org/apache/spark/sql/delta/GlutenDeltaParquetFileFormat.scala
  • forces TIMESTAMP_MICROS
  • switches to DeltaParquetWriteSupport for IcebergCompatV2

During investigation we also confirmed that Velox already supports explicit Parquet field_id assignment in its native Parquet writer.

Main gaps

• no delta-iceberg dependency/test enablement in Gluten build/test flow
• no end-to-end Velox UniForm test coverage
• no proof that native Delta write passes the nested field IDs required by IcebergCompatV2 into the native Parquet writer
• no explicit validation/fallback for unsupported cases such as active deletion vectors
• no supported-scope documentation beyond Not tested

Relevant Delta requirements

At minimum, the supported path needs:

• column mapping enabled
• minReaderVersion >= 2
• minWriterVersion >= 7
• delta.enableIcebergCompatV2=true
• delta.universalFormat.enabledFormats=iceberg
• Delta 3.1+ writer
• Hive Metastore-backed Iceberg catalog path
• no active deletion vectors
• partition columns materialized in Parquet
• numRecords populated in new AddFile stats
• timestamp columns written as int64 / micros
• nested array/map field IDs written into the Parquet schema

References

• Delta UniForm docs: https://docs.delta.io/delta-uniform/
• Delta protocol: https://github.com/delta-io/delta/blob/master/PROTOCOL.md