der: derive(Choice) needs `constructed = "true"` flag

derive(Choice) needs constructed = "true" flag,
but derive(Sequence) does not.

#[derive(Choice)]
pub enum ImplicitChoice<'a> {
    // This works:
    #[asn1(context_specific = "3", tag_mode = "IMPLICIT", constructed = "true")]
    SequenceOfNulls(SequenceOf<Null, 1>),

    // This won't decode:
    #[asn1(context_specific = "3", tag_mode = "IMPLICIT")]
    SequenceOfNulls(SequenceOf<Null, 1>),
}

I mean, the Choice macro is clueless about the underlaying type.

Something like this is possible:

let tag: Tag = Tag::Utf8String;
match tag {
    String::TAG => {}
    Null::TAG => {}
    SequenceOf::<Null, 1>::TAG => {}
    // .. more choices
}

Start at the Rust derive(Choice) macro, then compare how it determines tags and constructed status for SequenceOf with derive(Sequence). Reproduce the shown implicit SequenceOf<Null, 1> case and confirm decoding succeeds without the explicit flag; done means the Choice-derived case handles the underlying type consistently.