Fly Machines API on Runtime

Code written for Fly's Machines API now runs on Runtime by changing one address: run npx withruntime fly-api and point FLY_API_HOSTNAME (or fly-go's FLY_FLAPS_BASE_URL) at it. Each Machine is a sandbox; init, env, files, metadata, leases and the restart policy work, and what isn't supported is refused with Runtime's alternative. Node services can serve it themselves with machinesApi() from withruntime/fly. See switching from Fly Machines.