chore: relocate models dir

[francis2tm]

Introduction

To be more in line with huggingface's hub, let's store the models in cache_dir() instead of data_dir().

[francis2tm]

@toschoo additionally, I also suggest using here.
Or am I missing something?

[toschoo]

I'm not sure about this. I think that where we locate our models is the data dir, not the cache dir. HF might see it as the cache. But where it is located on the computer looks like a data dir. In fact, in our concept there is no cache dir. Calling it cache is somewhat confusing. After all, it's where users put their models. Anyway, we need to review all of this when we start working on the module manager.

[francis2tm]

We're going to stick with data_dir.