Function merge_materialize_metadata_into_iceberg_schema 

fn merge_materialize_metadata_into_iceberg_schema(
    materialize_arrow_schema: &Schema,
    iceberg_schema: &Schema,
) -> Result<Schema>

Merge Materialize extension metadata into Iceberg’s Arrow schema. This uses Iceberg’s data types (e.g. Utf8) and field IDs while preserving Materialize’s extension names for ArrowBuilder compatibility. Handles nested types (structs, lists, maps) recursively.