Function r_check_for_vec_element 

fn r_check_for_vec_element(elem_ty: &Type) -> Option<RTypeCheck>

Map a Vec<T> or &[T] element type to the appropriate vector type check.

Numeric elements produce VectorNumeric, bool produces Vector("logical"), String produces Vector("character"), etc. Handles nested Option<T> for nullable element types (e.g., Vec<Option<String>> becomes character vector).