store local cache in XDG_CACHE_HOME

[TheJolman]

Having it version controlled in this repo is a bit odd. Cache should be automatically overwritten when it becomes stale.

XDG_CACHE_HOME is usually ~/.cache, so we would be storing our cache at ~/.cache/oss-stas/stats.json or similar. We could use another xdg base dir (see https://wiki.archlinux.org/title/XDG_Base_Directory for more info), but I feel like this one makes the most sense.

[tomasohCHOM]

My idea with having it inside stats/stats.json was to make it visibly accessible for anyone looking at the repository, without having to run the CLI tool to see it. In hindsight, it probably makes sense to store it somewhere else outside of version control since the users running the tool will probably have to see the updated stats anyway, so I think this is a good change request