[Contribution suggestion] Allow explicitly passing in model_dir

[thogerb]

Hi @1adrianb

Lovely package, first of all. I was testing it, and ran into (and have resolved in a fork) an issue with deploying to AWS Lambda:

• AWS Lambda only allows IO writes to the /tmp/ directory namespace
• The current package defaults to the get_dir from torch.hub which is not within that namespace
• Result: No models run on AWS Lambda from what I can deduce

Fix/enhancement (easy): Add model_dir: str = None to each of the __init__ for classes that use torch URL-loading functions. Downstream functions already support the explicit model_dir, but top-level class initialization e.g. in api.py module doesn't.

If you agree, I am happy to send you a PR on it:)

Best, Thoger.

[thogerb]

Ok, I notice now that the same could probably also be achieved by globally calling torch.hub.set_dir or setting the TORCH_HOME environment variable.

Docs: https://pytorch.org/docs/stable/hub.html#torch.hub.get_dir

Personally not a big fan of using the global state but it should suffice for the use case 👍 Feel free to close this opened "Issue".