Add cached function to bolts

[samuelchassot]

No description provided.

[vkuncak]

Can we make cache field private:

final case class CachedFunction[I, O](
    f: I => O,
    hashable: Hashable[I],
    private cache: MutableHashMap.HashMap[I, O]
) 

and move these requires to the apply, because we have some issues with require on constructors?

  @opaque
  def apply(x: I): O = {
    require(cache.valid)
    require(CachedFunction.allValuesAreFunctionOutputs(f, cache))

[samuelchassot]

Indeed, good points! Here is another PR #98