Scan fails when an equality delete uses a nested field #3450

Apache Iceberg Rust version

main (1270e32)

Describe the bug

The spec allows equality delete columns nested under structs, and EqualityDeleteWriter accepts them (see the nested-field test in equality_delete_writer.rs). But reading such a delete file fails the scan with Unexpected => field not found: RecordBatchTransformer only maps top-level field ids (record_batch_transformer.rs:889).

To Reproduce

Table schema 1: f long, 2: s struct<3: f long>. Equality delete file with equality_ids = [3] and one row s.f = 7. Loading it through CachingDeleteFileLoader (evolve_schema, then parse) returns Err(Unexpected => field not found).

Expected behavior

The delete is applied to rows where s.f = 7, as for a top-level column.

Willingness to contribute

I can contribute a fix for this bug independently