Use custom concrete error types

[kamiyaa]

I haven't used anyhow much myself, but from what I read online, I think it makes more sense to have custom error types as a library.

I think it should also help with

• more concise errors
• easier mocking (at least for coral)
  • being able to create tests for all possible errors returned from secure-signer

https://www.reddit.com/r/rust/comments/gqe57x/what_are_you_using_for_error_handling/

[JasonVranek]

This is a pretty old post. I see a lot of rust Ethereum projects using https://github.com/eyre-rs/eyre which is a better fork of anyhow. We can switch to this in future but consider it low priority.