Support recursive record schemas

[vlovgr]

Codec.record does currently not support recursive types.

The following example:

import vulcan.Codec

final case class Recursive(next: Option[Recursive])

object Recursive {
  implicit def recursiveCodec: Codec[Recursive] =
    Codec.record[Recursive]("Recursive") { field => 
      field("next", _.next).map(Recursive(_))
    }
}

yields a StackOverflowError for Codec[Recursive].

scala> Codec[Recursive]
java.lang.StackOverflowError
  at scala.Option.fold(Option.scala:175)
  at vulcan.Codec$.record(Codec.scala:1468)
  at Recursive$.recursiveCodec(<pastie>:28)
  at Recursive$.$anonfun$recursiveCodec$1(<pastie>:30)
  at vulcan.Codec$.record(Codec.scala:1469)
  at Recursive$.recursiveCodec(<pastie>:28)
  at Recursive$.$anonfun$recursiveCodec$1(<pastie>:30)
  ...

Codec.derive also fails to derive a Codec with the following error message.

scala> Codec.derive[Recursive]
error: magnolia: could not find Codec.Typeclass for type Option[Recursive]
    in parameter 'next' of product type Recursive

[vlovgr]

I've had a brief look into this, and I believe it's going to be difficult to support in the current implementation. I'd generally recommend to avoid recursive schemas, as some systems are incapable of supporting them.