Backend: Caching decorator

[neubig]

We have caching utils: https://github.com/zeno-ml/llm-compare/blob/main/llm_compare/cache_utils.py

But using them can be a bit verbose and opaque.

It would be nice if we could add a decorator like this:

@cache_utils.cache_function("text_classification", load_model)

where the first argument is the task name, and the second argument is the function used to load from the cached files.

[neubig]

This might not be worth the effort now.