MkFieldLens.mkFieldLens returns a derived type instead of type parameter

[Lior Regev]

MkFieldLens.mkFieldLens[A, N <: Nat, R <: HList, B] returns an Aux[A, K, mkLens.Elem] instead of using MkRecordSelectLens.Aux[R, K, B] and return a Aux[A, K, B]

While this compiles just fine, it makes the job harder for static code analysis and intellij specifically is getting confused by it