Add support for PEP-561: type-hinting [smolagents]

[sugatoray]

PEP-561 suggests how to add support for type-hinting to a python library.

Note: I have already pushed a PR for this.

• Add support for type-hinting (PEP-561) #111

[aymeric-roucher]

Thank you for raising this @sugatoray ! Actually we don't want to signal type checkers that the repo is correctly typed, because it is not.
Check this comment for why we don't enforce PEP-561 in other Hugging Face repositories like transformers.