Inheriting from ZNB to support other R&S VNAs

Nobody has claimed this yet.

Hello! In https://github.com/microsoft/Qcodes/blob/d4e1e15de07c4d3a4cd94445dd614637d96aec31/src/qcodes/instrument_drivers/rohde_schwarz/ZNB.py#L1057, would it be possible to move
```
m_frequency = {
"ZNB4": (9e3, 4.5e9),
"ZNB8": (9e3, 8.5e9),
"ZNB20": (100e3, 20e9),
"ZNB40": (10e6, 40e9),
}

```
outside of the init so that it becomes a class attribute that we can override, and then in the init just do
```
if model not in self.m_frequency.keys():
raise RuntimeError(f"Unsupported ZNB model {model}")
```

The same question would hold for
```
self._model_min_source_power = {
"ZNB4": -80,
"ZNB8": -80,
"ZNB20": -60,
"ZNB40": -60,
}
```
in https://github.com/microsoft/Qcodes/blob/d4e1e15de07c4d3a4cd94445dd614637d96aec31/src/qcodes/instrument_drivers/rohde_schwarz/ZNB.py#L440C1-L445C10

If this were the case, we could inherit from these classes and add support (in our local codebase, not asking you to support them explicitly!) for other R&S VNA's, such as the ZNL and the ZNLE. These VNA's follow the exact same programming as the ZNB but have different ranges for their frequencies and powers, for which right now we have to copy & paste most of the ZNB driver and adjust these few lines.

Open src/qcodes/instrument_drivers/rohde_schwarz/ZNB.py at the referenced frequency-range and minimum-source-power sections, then inspect ZNB initialization and model validation. Done means the model-specific values are overridable at class level, unsupported models still raise the stated RuntimeError, and subclasses can provide ranges and powers for other Rohde & Schwarz VNAs.

Written by the indexing model from the issue text.