Cache of k3s download for faster re-install (or --reset?)

Setting up a 5 node cluster, developing, wiping out the cluster via uninstall and then re-installing is slow.

The thought was that with an added `--cache` option the k3s download would be stored in /tmp. It would remain if the uninstall command was also called with `--cache`. That way, during the next install with `--cache` it will check to see if the file already exists in /tmp by verifying the sha256sum against the previously downloaded file to verify integrity and re-install without re-downloading.

```
[INFO] Downloading hash https://github.com/k3s-io/k3s/releases/download/v1.30.5+k3s1/sha256sum-amd64.txt
[INFO] Downloading binary https://github.com/k3s-io/k3s/releases/download/v1.30.5+k3s1/k3s
```

If there's a more eloquent way to reset a 5 node HA cluster back to the state right after it was installed, perhaps with a `--reset` option instead? I'd be even more interested in that approach!

## Do you want to work on this?

Subject to design approval, are you willing to work on a Pull Request for this issue or feature request?

I'm not even sure where to begin, so probably not.