Native Iceberg scan fails a VERSION AS OF read of a column whose type was promoted after the snapshot #6993

Describe the bug

A VERSION AS OF read of a column whose type was promoted after the snapshot (int to bigint, float to double, a wider decimal, including a nested field) fails in the native Iceberg scan. Spark returns the snapshot's values.

CREATE TABLE t (id INT, x INT) USING iceberg;
INSERT INTO t VALUES (1, 10);
-- take snapshot S here
ALTER TABLE t ALTER COLUMN x TYPE BIGINT;
SELECT id, x FROM t VERSION AS OF S;

org.apache.comet.CometNativeException: Batch adaptation failed: External error: Parquet column cannot be converted in file . Column: [[x]], Expected: int, Found: INT64

Reproduced on main at 7d8d9b1 (Spark 4.1, Iceberg 1.11). branch-1.1 has the same task-schema code.

Spark reads a time travel query with the snapshot's schema, so x is int. The native task reads with the current table schema instead: tableSchema for a task without deletes, and task.schema() for a task with deletes. iceberg-rust then returns x as bigint, and the batch adaptation refuses to narrow it back. When a projected column was dropped after the snapshot, a task without deletes reads the scan schema instead, and the query works.

#6725 (open) makes the native scan read the pruned scan schema by default, which fixes this for scans that can prune. branch-1.1 needs its own fix.

Steps to reproduce

See above. Tasks with position deletes, an identity partition source projected after its promotion, and a promoted nested field (s.a) fail the same way.

Expected behavior

The native scan returns the snapshot's values with the snapshot's types, as Spark does.