noble-ed25519 VS signature-sdk-js

[For reference, see section 7.8](https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.186-5-draft...).

I've also been looking for Ed25519ph support for other languages. [Paul Miller](https://github.com/paulmillr), who is the author of the noble libraries for Javascript has just added support in his newly released [curves](https://github.com/paulmillr/noble-ed25519/issues/63) library. Paul has suggested on Twitter holding off on using "curves" until an audit, but most of his other work has already been audited and all his works are highly polished.

Also, for all readers, we wrote an [online Ed25519 tool](https://cyphr.me/ed25519_applet/ed.html), which is useful for testing and verifying. Previously the top result on Google, which has now been taken down, was sending the keys off to a server, which motivated us to write a tool that didn't openly phone home.

(Git hashes the repo and provides version history. It's not "super secure", but it is much better than nothing. I could also sign releases, but I'm not doing that at the moment, since I don't think the marginal benefit is there, especially since Paul is signing the crypto part already.)

To provide some context, I generate the signature image on the frontend using a sign pad (Wacom STU430) through the JavaScript library signature-sdk-js, also from Wacom. This library takes the PDF document from my Ruby backend as input and produces two output files: the PNG image of the signature and a specific ISO file. This ISO file, from what I understand, utilizing the PDF hash, ensures the secure linkage between the signature and the PDF.