Option to select model

First of all, thanks for creating the plugin! Very simple, very useful.

Maybe I'm missing some config but is it possible to customize the model it uses? Since codex [already supports](https://arc.net/l/quote/rizqlrss) this:

```bash
$ codex -m o3
```

Something like this would be nice:


```lua
opts = {
  model = 'o3-mini'
}
```