[substrait]: schema roundtrip fails

[niebayes]

Describe the bug

If a DataFusion schema contains a timestamp column with timezone other than "UTC", the roundtrip fails.
Specifically, converts the schema to substrait named struct and then converts the named struct back to schema, the reconstructed schema will always have a timestamp column with timezone being "UTC", other than the original timezone.

To Reproduce

The following test fails. Note, there's a timestamp column with non-UTC timezone.

#[test]
fn named_struct_names() -> Result<()> {
    let schema = DFSchemaRef::new(DFSchema::try_from(Schema::new(vec![
        Field::new("int", DataType::Int32, true),
        Field::new(
            "struct",
            DataType::Struct(Fields::from(vec![Field::new(
                "inner",
                DataType::List(Arc::new(Field::new_list_field(DataType::Utf8, true))),
                true,
            )])),
            true,
        ),
        Field::new("trailer", DataType::Float64, true),
        Field::new("time", DataType::Timestamp(TimeUnit::Second, None), true),
        Field::new(
            "time_with_tz",
            DataType::Timestamp(TimeUnit::Second, Some("+00:00".into())),
            true,
        ),
    ]))?);

    let named_struct = to_substrait_named_struct(&schema)?;

    // Struct field names should be flattened DFS style
    // List field names should be omitted
    assert_eq!(
        named_struct.names,
        vec!["int", "struct", "inner", "trailer", "time", "time_with_tz"]
    );

    let roundtrip_schema =
        from_substrait_named_struct(&test_consumer(), &named_struct)?;
    assert_eq!(schema.as_ref(), &roundtrip_schema);
    Ok(())
}

Expected behavior

No response

Additional context

No response