Function core_to_binding_match_arm 

pub fn core_to_binding_match_arm(
    core_prefix: &str,
    variant_name: &str,
    fields: &[FieldDef],
) -> String

Generate a match arm for core -> binding direction. Core enums may have data variants; binding enums are always unit-variant-only. For data variants: CoreEnum::Variant(..) => Self::Variant