`ValidationError` & `ValidationErrorKind::Invalid` is useless without information of what the invalid value and what type was expected

`ValidationError` & `ValidationErrorKind::Invalid` is useless without information of what the invalid value and what type was expected.

Both types derive traits which would break if we added extra information:

https://github.com/duesee/imap-codec/blob/086523d64095fd7da35b4fe5ffe27067185c9801/imap-types/src/error.rs#L9-L13

But is a validation error really equal to another validation error if the value domain and/or the value are different? 🤔 Do these errors need to be hashable/orderable/comparable?