Define ST_F8_E8M0

[pcuenca]

Opening for discussion. I saw #3374, so perhaps this should go there instead. The goal is just to be able to load the native DeepSeek V4 safetensors files, since the attention scales use F8_E8M0.

If this direction is ok, I'm happy to add tests or update docs as needed.

Proposed changes

Define ST_F8_E8M0 so loading safetensor files that include this type succeed. Handling would be deferred to sanitize functions in mlx_lm and other user code.

Checklist

Put an x in the boxes that apply.

• I have read the CONTRIBUTING document
• I have run pre-commit run --all-files to format my code / installed pre-commit prior to committing changes
• I have added tests that prove my fix is effective or that my feature works
• I have updated the necessary documentation (if needed)

[zcbenz]

Looks good to me!

Adding test is tricky because the from_fp8/to_fp8 ops assume e4m3, we could extend the APIs to e8m0 but I think maybe we should just add fp8 support instead. So I'm good with no test for this one.

[pcuenca]

So I'm good with no test for this one.

👍 Sounds good!

I searched for type mentions in the docs but I found nothing to update either. Let me know if anything else is missing.