GLiNER2 support

The GLiNER2 paper was released recently: https://huggingface.co/papers/2507.18546

There is also already a demo by the authors, but it currenlty uses private models: https://huggingface.co/spaces/fastino/random-demo

We would want to support GLiNER2 asap after public release.

Adding support for the new features besides NER (text classification & structured extraction) is a second priority.