Is your feature request related to a problem or challenge? Please describe what you are trying to do.

Given data like:

{"user": {"id": 123, "metadata": {"tags": ["a"], "score": 95.5}}}

Users want to extract user with:

• id as Int32
• metadata as Variant (not expanded)

Currently, this requires multiple variant_get calls and manual StructArray assembly.

Describe the solution you'd like

Use ExtensionType to mark fields that should remain as Variant:

let field = Field::new("user", DataType::Struct(Fields::from(vec![
    Field::new("id", DataType::Int32, true),
    Field::new("metadata", ..., true).with_extension_type(VariantType),  // Keep as Variant
])), true);

let result = variant_get(&array, GetOptions::new().with_as_type(Some(Arc::new(field))))?;