Improve implicit resolution of validated mapping

[koshelev]

No description provided.

[simao]

I think we should keep this separate. The problem is when you have multiple valid implicits, scala is not always smart enough to tell you there are too many and it cannot choose one. In the past, this led to cases where the app was using the wrong implicit.

For example, if there is a circe encoder for type T and a Validated mapper for type T, which should be used? there is a mapping for json types and there is a mapping for validated so..

[koshelev]

this PR just get's rid of validatedStringMapper[T], so nothing changes in regards of your concerns. validatedStringMapper[T] should go away in any case.
It always makes sense to pass parameter explicitly in case there are multiple implicits for the same type. But it should not be a case for wrapper types anyway.

[houcros]

It seems BookTitle is not defined?

[houcros]

I pushed a new commit with the definition.