Add multiple `Var` operations in example `CRTest`

[ronanM]

Add operations with multiple Var in hedgehog.examples.state.CRTest, to explain how to mix operations with single Var and operations with multiple Var in the model.

For example:

def createList(vs: List[String]): List[CRId]

def readList(ids: List[CRId]): List[Option[String]]

Maybe related with:

• State machine testing multiple results haskell-hedgehog#113

I don't know how to write in Scala this trick:

• Return multiple Vars from a single Command haskell-hedgehog#459 (comment)

[ronanM]

Bad first attempt:

• CRMultipleTest