Allow passing throw a cache retention time and setting a non-infinite default

[seabbs]

At the moment we never invalidate the cmdstan cache but this appears to be causing issues on certain platforms (for example MacOS). Its unclear to me why this happening but a simple solution would be to default to only keep the cache for a few days (perhaps a week) and allow the user to set this. I think this would better balance the speed you get from caching with robustness.