Duplicate field ids inside a struct are not validated when the file schema equals the requested schema and no predicate is pushed

[dwsmith1983]

Describe the bug

Comet validates Parquet field id lookups in the physical expression adapter, which resolves each file's mapping once per file (#5654). DataFusion 55's Parquet opener skips the adapter entirely when the file's physical schema compares equal to the logical schema and there is no pushed predicate. In that case a file whose struct carries two children with the same field id is read positionally instead of failing with Spark's duplicate field id error.

Spark-written files always carry key-value metadata that arrow-rs folds into the physical schema, so they never compare equal and always reach the adapter. The gap is limited to files with no key-value metadata at all, read with field id matching enabled and no data filter.

Steps to reproduce

1. Write a Parquet file without key-value metadata whose schema is s<x: long id=1, y: long id=1> (parquet-mr with a hand-built MessageType).
2. Read it with the native scan, spark.sql.parquet.fieldId.read.enabled=true, and a requested schema identical to the file schema, with no filter.
3. Spark rejects the duplicate id during schema clipping; Comet returns the rows.

Expected behavior

The duplicate field id error, as when a cast or predicate is present.

Additional context

Found in review of #5654, where the once-per-file validation was added. The short circuit is in DataFusion's opener, so the fix is either a Comet-side check before the opener decides, or an upstream option to always run the adapter.

[dwsmith1983]

@andygrove I will do this as well.