ci: many improvements to the ci

Description

This PR contains many improvements to the CI.

Modify the CI to add testing of Jupyter notebooks (ensuring they run successfully)
Modify the CI to ensure that Jupyter notebooks are clean (no cell output)
Improve the performance of the CI by caching Python client wheels
Modify the CI to ensure Rust code is properly formatted
Add an action to run precommit hooks as part of the CI (this will ensure Python code is formatted with black, and pass flake8)

While introducing these new checks, I updated the codebase when needed so that it could pass the CI. Code changes include:

Reformatting Rust code
Fix all notebooks. When the multiple models feature (commit: 9ec02771398e39e2f8de7160f62050f1ad1b9bad) was introduced, the client interface changed in a backward incompatible way. Since then the notebooks can not run with the BlindAI client version you get by building from source. I updated the notebooks to make them work again.
Adding cells to the Jupyter notebooks to remove the updated model when finished (else the CI would fail likely because of memory exhaustion). This also has the benefit of showing how to use this new feature.

This change affects the CI.