fix torchao quantizer for new torchao versions (#12901)
* fix torchao quantizer for new torchao versions
Summary:
`torchao==0.16.0` (not yet released) has some bc-breaking changes, this
PR fixes the diffusers repo with those changes. Specifics on the
changes:
1. `UInt4Tensor` is removed: https://github.com/pytorch/ao/pull/3536
2. old float8 tensors v1 are removed: https://github.com/pytorch/ao/pull/3510
In this PR:
1. move the logger variable up (not sure why it was in the middle of the
file before) to get better error messages
2. gate the old torchao objects by torchao version
Test Plan:
import diffusers objects with new versions of torchao works:
```bash
> python -c "import torchao; print(torchao.__version__); from diffusers import StableDiffusionPipeline"
0.16.0.dev20251229+cu129
```
Reviewers:
Subscribers:
Tasks:
Tags:
* Apply style fixes
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