SDNQ support

### Feature Idea

[SDNQ](https://github.com/Disty0/sdnq) provides low bit quantization with good quality and performance. Incorporating it for on-the-fly quantization and loading pre-quantized models would be great, especially for larger models like flux.2 where fp8 is too large, even for 24GB gpus. I have tried writing a custom node for this, but failed due to the model and vram management getting in the way. Compared to nunchaku this approach doesn't depend on a custom model implementation from another dev team for each new model.

### Existing Solutions

[ComfyUI-SDNQ](https://github.com/EnragedAntelope/comfyui-sdnq) is a vibe coded custom node that doesn't actually work

### Other

_No response_