[Feature Request]: Implement scheduler selection independent of sampler a la A1111

### Is there an existing issue for this?

- [X] I have searched the existing issues and checked the recent builds/commits

### What would your feature do ?

See https://github.com/AUTOMATIC1111/stable-diffusion-webui/pull/15333

The sampler dropdown is getting a little ridiculous in length now (especially on dev2), and we are arbitrarily limited from selecting certain sampler/scheduler combinations (i.e. DPM++ 3M SDE AYS).

Would be a lot better to implement a separate dropdown for scheduler selection, similar to what A1111 has done recently-ish.

### Proposed workflow

1. Go to ....
2. Press ....
3. ...
4. ???
5. Profit

### Additional information

_No response_

Start by reviewing the linked A1111 pull request and tracing the existing sampler-selection flow in Forge. Confirm how sampler and scheduler combinations are currently represented, then define completion as separate sampler and scheduler controls that permit combinations such as DPM++ 3M SDE AYS while reducing the sampler dropdown length.

Written by the indexing model from the issue text.