flush fs access on Drop

[yoshuawuyts]

We should probably implement the Drop trait so when we destroy the rad instance, we can call the fs.sync (forgot the name) method to make sure everything has been persisted to disk.

@spacejam warned we're opening us up for trouble if we don't ensure this is called 🙏

[spacejam]

This is an area that is pretty hard to get right:
https://danluu.com/file-consistency/

It's lower priority if your stuff doesn't need to actually be on the machine after an abrupt restart, but to the extent that your data can't be found elsewhere or recomputed from something that can be, this is worth thinking about.

I'm happy to help with this :)

[yoshuawuyts]

@spacejam ohh, yeah that link is real helpful. I think we definitely will want to handle data persistance as well as possible - help would be real good with this! :D