Add e_init restrictions and defaults to PANTHER

The PANTHER instrument in AbINS has restrictions on its `e_init` values which have not yet been implemented in ResINS:

```
        "min_wavenumber": 0.0,
        "max_wavenumber": 150 * MILLI_EV_TO_WAVENUMBER,
```

and similarly for the default:

```
        "e_init": 150 * MILLI_EV_TO_WAVENUMBER,
```

Might be a good idea if this waits for #23 