`EnrError` should implement `std::error::Error`

[adoerr]

EnrError currently is a plain struct.

IMO, this is a bit non-idiomatic. Especially conversion into other custom error types is more involved than it should be. For example, thiserror offers a #[from] attribute which auto-generates a From implementation. This, however, expects the source error type to implement std::error::Error.

As an alternative, we could just derive thiserror::Error which will generate a std::error::Error implementation.

WDYT?

[AgeManning]

Sure, Don't mind implementing the std::error::Error trait. Will add it in