Add type stubs for lib.rs

[baranyildirim]

TLDR: Add type stubs for most of the code in lib.rs

Without type stubs, this library is quite hard to integrate into projects that have type-checking enabled.
Added type stubs based on the Rust types and documentation in lib.rs

Couldn't find an easy way to add types to Term (PyTerm). It is currently Any typed as a result.
All the code in biscuit_test.py now passes type checking with PyRight, so I assume the types are working correctly.

[divarvel]

Thanks, that's really valuable! Is there a way to add a relevant check in CI?

Could you drop the commit that reformats tests please? As long as there is no automatic formatting in this project I'd prefer PRs to be limited to actual changes.

(what formatter do you use? I would be open to a dedicated PR formatting the codebase and enforcing it in a dedicated CI step).

[baranyildirim]

Thanks, that's really valuable! Is there a way to add a relevant check in CI?

There is but we would have to pick a type checker (pyre, mypy, pyright etc.) and add that to CI. Something like this: https://github.com/marketplace/actions/mypy-action

Could you drop the commit that reformats tests please? As long as there is no automatic formatting in this project I'd prefer PRs to be limited to actual changes.

Done!

(what formatter do you use? I would be open to a dedicated PR formatting the codebase and enforcing it in a dedicated CI step).

I was using Black.

[divarvel]

Alright, thanks! I guess we can add a new step in the existing github actions to run mypy on biscuit_test.py (I have tried quickly to trigger a type error but haven't succeeded)

[divarvel]

i will setup black in a follow up PR

[baranyildirim]

Alright, thanks! I guess we can add a new step in the existing github actions to run mypy on biscuit_test.py (I have tried quickly to trigger a type error but haven't succeeded)

Added mypy action in the Build & Test workflow.