[71,72] Track item moving between vaults and requests rate limits

Hey kovpack

I don't think we do a great job of explaining how the cache works, and I think we want to do a better job documenting it moving forward, but for now, I think I can take a shot at some of your questions.

Before I start my explanation, I would just like to note that the Windows op client does not support any caching and instead silently fetches all objects directly from the server even when the --cache flag is specified.

The cache works by creating an in-memory store that stores encrypted vault items. We spawn a subprocess that manages it. The inactivity timeout of this process and its in-memory cache can be set by the op daemon command along with the --timeout option, but defaults to 24 hours if unspecified.

We use a lazy-sync method to determine whether or not the cached item is no longer up-to-date. That is, every time an item is retrieved with the --cache flag enabled, we check whether its cached version is the same as what we have stored in our servers. If the server version has been updated, we fetch the new item and store it in the cache. So regardless of whether or not you specify the --cache flag, we will retrieve the most up-to-date version of it.

When the item in the cache happens to be up-to-date, we deliver it faster than having to fetch the whole item from the server.

I hope this makes sense, and please do not hesitate if you have any followup questions!