model-conversion : add device option to run-org-model.py (#18318)

model-conversion : add device option to run-org-model.py (#18318)

* model-conversion : add device option to run-org-model.py

This commit refactors the `run-org-model.py` script to include a
`--device` argument, to allow users to specify the device on which to
run the model (e.g., cpu, cuda, mps, auto).
It also extracts a few common functions to prepare for future changes
where some code duplication will be removed which there currently
exists in embedding scripts.

The Makefile is also been updated to pass the device argument, for
example:
```console
(venv) $ make causal-verify-logits DEVICE=cpu
```

* fix error handling and remove parser reference

This commit fixes the error handling which previously referenced an
undefined 'parser' variable.