This PR will introduce Python bindings for the ooniauth-core crate

The bindings are implemented in the ooniauh-py crate, using pyo3 and maturin to make the bindings

My main goals with this crate were:

• A thin abstraction over ooniauth-core, so that the usage of the library is driven by that crate
• Idiomatic and well-typed Python to make it easier to work with from the Python side
• making a testing UserState class for testing with Python
• Being able o reproduce the basic usage example from python

In the following repo I provide a minimal fastapi project to show how the library will be used in Python: https://github.com/LDiazN/anoncred/blob/main/tests/test_creds.py (Still WIP)

Note: the fastapi project assumes that you have the library installed in your virtual environment, this is due to how the maturin workflow works (it assumes that you are running in a virtualenv, and during development it installs the preview library in that virtualenv)

Feedback

The intention with this first iteration is to lay the foundational work to direct the development of the bindings library, so all the feedback is welcome

That said, here are some things that I think might need a bit more thought:

• bytes interface? : If you look at the example usage here and here the Python client still needs to perform to_bin and to_str conversions for transfers. This is because we're using json as encoding, so we could change the encoding to keep the bytes interface if we really need it, but if there's no reason to keep it, I would say we change it to a string interface (and it's probably more efficient to do those conversions in Rust land anyways)
• Exception handling: In exceptions.rs you can see the different exception types we have in Python, these are mappings from our errors to Python exceptions. We might want to think a bit more about how we want to represent this errors

closes #6