Add AutoModel support

[not-lain]

About this feature

I think it would be highly useful to add AutoModel support to the current library.
Something that goes like

from mlx_vlm import AutoModel 

model = AutoModel.from_pretrained("hf_repo_or_path")

Auxiliary info

I was able to get this feature running on pxia by checking the model_info first (specifically the repo tag which is stored in the readme file) then calling the appropriate model architecture

I'm not currently in possession of any mac resources so i can't work on this, but feel free to reach out if you have any further questions.

[not-lain]

additionally if you want to make the file download more optimized i can share this interesting resource HF's PyTorchModelHubMixin as well