coerce_int96 leaves INT96 in two-level and legacy Parquet lists as nanoseconds #26463

Describe the bug

With datafusion.execution.parquet.coerce_int96 set, INT96 timestamps inside lists that do not use the three-level LIST layout stay Timestamp(Nanosecond, None). That covers Hive's two-level lists (repeated int96 bag, how Hive writes array<timestamp>), bare repeated int96 fields, and parquet-mr Avro's legacy lists whose repeated group is named array. Values outside 1677-09-21 to 2262-04-11 then overflow on decode, which is what coerce_int96 is meant to prevent: 0001-01-01T01:02:03.123456 reads back in 1754.

To Reproduce

use std::sync::Arc;
use arrow::datatypes::TimeUnit;
use datafusion_datasource_parquet::Int96Coercer;
use parquet::arrow::parquet_to_arrow_schema;
use parquet::schema::{parser::parse_message_type, types::SchemaDescriptor};

let descr = SchemaDescriptor::new(Arc::new(
    parse_message_type(
        "message m {
          optional group hive (LIST) { repeated int96 bag; }
          optional group three (LIST) { repeated group list { optional int96 element; } }
        }",
    )
    .unwrap(),
));
let arrow_schema = parquet_to_arrow_schema(&descr, None).unwrap();
let coerced = Int96Coercer::new(&descr, &arrow_schema, &TimeUnit::Microsecond)
    .coerce()
    .unwrap();
println!("{:?}", coerced.field_with_name("hive").unwrap().data_type());
println!("{:?}", coerced.field_with_name("three").unwrap().data_type());

hive keeps Timestamp(Nanosecond, None) while three becomes Timestamp(Microsecond, None).

Expected behavior

Every INT96 leaf coerces to the requested unit, whatever the list encoding.

Additional context

coerce_int96_to_resolution_impl in datasource-parquet/src/schema_coercion.rs finds INT96 leaves by rebuilding each Arrow leaf's Parquet path, and assumes a list's path is <list>.list.<element>. For hive it looks up hive.list.bag, which no column has, since the path is hive.bag. It also never descends LargeList or FixedSizeList.

Willingness to contribute

I plan to contribute a fix for this bug independently