Expose try_cache + create_recycled_thread publicly

[cheesycod]

I currently have ~50-100 lines of code to do exactly what the (private) Chunk::try_cache method does but worse. It would be nice if Chunk::try_cache could be exposed as such.

Also, is there a reason lua.create_recycled_thread is private, would be nice to have this available (it would be a useful performance optimization (even if exposed as an unsafe function) for my custom more-roblox-geared async scheduler thing that I've been working on )