strip_metadata_from_schema fails on list and map columns

[NoahKusaba]

Apache Iceberg Rust version

main (8cb2ade), 0.10.1

Describe the bug

iceberg::arrow::strip_metadata_from_schema returns an error for any Arrow schema that contains a list or map column:

Unexpected => Field stack underflow in list

MetadataStripVisitor remembers each field's name and nullability by pushing onto field_stack in before_field, and pops it when rebuilding the field in list, map, struct and primitive. But visit_list and the map arm of visit_type call before_list_element, before_map_key and before_map_value for the inner fields, not before_field. The visitor doesn't override those hooks, so rebuilding a list element or a map key or value pops from an empty stack.

The only test of this function is the doctest, which uses a flat schema, so this wasn't caught.

Downstream, datafusion-iceberg calls this function to validate INSERTs into partitioned tables, so an INSERT into a partitioned table with a list or map column fails (found in apache/datafusion-iceberg#19).

To Reproduce

use std::sync::Arc;

use arrow_schema::{DataType, Field, Schema};
use iceberg::arrow::strip_metadata_from_schema;

let schema = Schema::new(vec![Field::new(
    "l",
    DataType::List(Arc::new(Field::new("element", DataType::Int32, true))),
    true,
)]);
strip_metadata_from_schema(&schema).unwrap(); // Field stack underflow in list

Expected behavior

It returns the same schema with metadata removed at every level, including list elements and map keys and values.

Willingness to contribute

I can contribute a fix for this bug independently