dishmaker

der: use Cow for *Ref types

3

Following https://github.com/RustCrypto/formats/pull/1778#issuecomment-2840198645, we need to investigate why Cow does not work. One major issue is that `Clone` is implemented on `Ref` types. https://github.com/RustCrypto/formats/blob/217b6eff7bf1b15d4fea21a3a186c2faee4a4344/der/src/asn1/ia5_string.rs#L37-L40 which collides with (if i remember correctly):...

`derive(Choice)` needs `constructed = "true"` flag, but `derive(Sequence)` does not. ```rust #[derive(Choice)] pub enum ImplicitChoice {} Null::TAG => {} SequenceOf::::TAG => {} // .. more choices } ```