Introduce Temporary.using for ensuring directory cleanup after use

Raised from Ivory [PR comment](https://github.com/ambiata/ivory/commit/79699cfcf8c80b77000865c8108036425249684c#commitcomment-6873287)

/cc @markhibberd @maxpow4h 
Very true. Cool, I kinda prefer having per-test temp directories. Although feels like we could remove _more_ of the boilerplate by having a `List[Temporary => ResultTIO[Boolean]]` method, but I'll leave that one for another day.