Attribute Macro hax_frontend_exporter::prelude::derive_group

#[derive_group]

A proc macro unrelated to adt-into: it is useful in hax and we don’t want a whole crate only for that helper.

This proc macro defines some groups of derive clauses that we reuse all the time. This is particularly interesting for serializers and deserializers: today we use bincode and serde, but maybe we will want to move to something else in the future.