Replace derive_more (and remove syn 1.0 in favour of 2.0)?

[jsdw]

https://crates.io/crates/derive_more hasn't had a release in a couple of years, and particularly it's still using syn 1.0. Is there a sensible alternative?

We mainly use it for Display impls and mainly on error types (which derivative and derive_where don't offer) to be no-std friendly (we previously used thiserror for this, but it's not no-std friendly). We have a couple of From impl uses too.

I recently replaced derivative with derive-where for a similar reason; it hadn't seen a release in 3 years, was triggering non-canonical compiler warnings with some of its impls, and was still using syn 1.0. Would be good to eliminate syn 1.0 from the dependency tree entirely or as much as possible :)