[AURON #2527] Populate identity partition values in native Iceberg scans

[lyne7-sc]

Which issue does this PR close?

Closes #2527

Rationale for this change

Imported partitioned files can omit identity partition columns. Native Iceberg scans may return NULL for these columns instead of the values available in Iceberg partition metadata.

What changes are included in this PR?

• Populate identity partition columns from partition metadata by field ID for regular and changelog scans.
• Fall back to Iceberg when scan tasks require different sets of identity partition columns.
• Fix the test configuration so reference queries actually disable Auron, and verify the reference and native scan plans.

Are there any user-facing changes?

Native Iceberg scans correctly return identity partition values when the columns are absent from the data files.

How was this patch tested?

Compare Auron with Iceberg's reader using Parquet and ORC files that omit identity partition columns. Cover string, date, decimal and NULL values, projections, filters, metadata columns and changelog queries.

Was this patch authored or co-authored using generative AI tooling?

• Yes
• No

If yes, include: Generated-by: OpenAI Codex (GPT-6)

ASF guidance: https://www.apache.org/legal/generative-tooling.html