Removing multiple running images is broken

### Description

When `someimage` is currently in use by a container, `nerdctl rmi -f someimage` will create a new unnamed image (name: `:`) so that we keep a ref on the layers (though this is currently buggy, see #4107).

But then, trying to remove multiple such images will fail, as image creation will bail out (`image ":": already exists`).

Does anyone have a suggestion on how to address this?
Is there a way to instruct containerd to create an image without a name? (eg: currently, passing en empty name will fail on creation)

### Steps to reproduce the issue

```
nerdctl run -d debian sleep inf
nerdctl run -d alpine sleep inf
nerdctl rmi -f alpine
nerdctl rmi -f debian
```

### Describe the results you received and expected

```
FATA[0000] 1 errors:
image ":": already exists
```

### What version of nerdctl are you using?

main

### Are you using a variant of nerdctl? (e.g., Rancher Desktop)

None

### Host information

_No response_