`Cause#toString` is not stack-safe

Repro:

```scala
import zio.*

object Foo extends ZIOAppDefault {
  def works = ZIO.foreachParDiscard(1 to 1_000_000)(_ => ZIO.fail("Boom")).fold(_.toString, identity)

  def run = ZIO.foreachParDiscard(1 to 1_000_000)(_ => ZIO.fail("Boom")).foldCause(_.toString, identity) // SO error
}
```