Migrate from proc-macro-error to... ?

Please check out https://rustsec.org/advisories/RUSTSEC-2024-0370

It advises using one of the following crates instead:

* [manyhow](https://crates.io/crates/manyhow)
* [proc-macro-error2](https://crates.io/crates/proc-macro-error2)
* [proc-macro2-diagnostics](https://github.com/SergioBenitez/proc-macro2-diagnostics)