Investigate Rustacean crypto APIs about parsec-client-rust

[ionut-arm]

My opinion is still that we could benefit from integrating the RustCrypto Developers crates into this client. More precisely, for signing we could implement the traits defined here.

[hug-dev]

For integration with Rustls it would also be nice to investigate implementing their traits for siging with a key that is managed by Parsec: https://docs.rs/rustls/0.18.1/rustls/manual/_03_howto/index.html#customising-private-key-usage

[ionut-arm]

If we do this, we should probably split the implementations into different files to make it more scalable. Also, looking at those traits, they're fairly abstracted, so they would be used at least one layer above CoreClient, more likely at the "last level", where user involvement would be quite low ("just sign this data, please, don't care with what or how")

[ionut-arm]

Google also released a crate that is "difficult to misuse": https://crates.io/crates/mundane

They don't have any dependents, though, don't know if it's just something they use internally.

[hug-dev]

I don't know if it makes sense to keep this issue open. We can add specific ones for the specific things we would like to add in the future, if there is a need.