how to use Machines as a standard disposable VM

Hello! I want to use a Fly Machine in the same way that I would use something like Digital Ocean. That is, I want to have a machine that I can ssh into and install packages with apt and have multiple Unix users and run Docker Compose stacks and all that good stuff. However, starting a long-lived Machine using something like this:

fly m run -a unpleasable sleep infinity
fly ssh console -a unpleasable

… creates a machine that is unlike a standard virtual machine! systemd won’t work, the filesystem is not persistent, etc etc.

I know this is probably all expected given the goals of Fly, but I’d love it if I could do this because it would make moving some development environments over to Fly much more fun. Spinning up VMs on other hosting providers is terribly slow, and I’d love to be able to spin up a box super fast like Fly Machines allows.