Add an LRU cache to !wolfram thread checks

[TRManderson]

Currently, every time a response is posted in a thread visible to uqcsbot, there's an attempted API call by !wolfram. This should only happen on threads initiated by !wolfram.

For a fix that works now, but also works if we ever get to the point conversations.history actually works, we should cache a list of threads that are not initiated by !wolfram. We should also mark failed API calls as "not a wolfram thread" (possibly with a retry count or filtering on failure type) to minimise API requests we know for sure will fail.