Function write_nested_scalar_list 

pub fn write_nested_scalar_list(
    builder: &mut BufferBuilder<'_>,
    field_name: &str,
    inner: &TypeRepr,
    items: &[Value],
) -> Result<(), BufferError>

Marshal a nested List<List<scalar>> arg / schema field into field_name’s tail area, given the inner element TypeRepr and the outer Value::List items (each element itself a Value::List of inline-fixed scalars). Shared by both compiled backends so they emit byte-identical input buffers. Inner pointer-array element lists (List<List<String>> / List<List<Schema>>) are rejected by the layout pass before reaching here; this routine only handles the inline-fixed innermost elements (Int / Float / Bool).