Unable to convert Arrow Dictionary types to Iceberg schema

[phillipleblanc]

Apache Iceberg Rust version

0.4.0 (latest version)

Describe the bug

When converting an Arrow schema with a Dictionary type, I get an error that the conversion isn't possible.

To Reproduce

let arrow_type =
                DataType::Dictionary(Box::new(DataType::Int8), Box::new(DataType::Utf8));
            let iceberg_type = Type::Primitive(PrimitiveType::String);
            assert_eq!(iceberg_type, arrow_type_to_type(&arrow_type).unwrap());
            assert_eq!(DataType::Utf8, type_to_arrow_type(&iceberg_type).unwrap());

Expected behavior

The conversion proceeds with the inner dictionary type.

Willingness to contribute

I can contribute a fix for this bug independently