Inference Toolkit incompatible with transformers 5.x (is_tf_available import path changed) - due to strict transformers pin.

Inference Endpoints fail when any dependency requires `transformers>=5.0` due to deprecated import paths.
```
ImportError: cannot import name 'is_tf_available' from 'transformers.file_utils'
```

The toolkit imports from `transformers.file_utils`, which was removed in transformers 5.0. These now live in `transformers.utils`.

**Example**:
Deploying [GLiNER](https://github.com/urchade/GLiNER) (`gliner>=0.2.23` requires `transformers>=4.57.3`) fails on Inference Endpoints even with a custom handler that doesn't use the toolkit directly.

1. Can the import paths be updated for transformers 5.x compatibility?
2. Why does the toolkit pin `transformers==4.51.3` exactly? This strict pinning will likely cause conflicts with many libraries.