📦 setup Python packaging

[danielgafni]

Hey!

I noticed you project was not installable as a Python package, meaning it was not possible to run something like pip install git+http://github.com/antoinelame/GazeTracking.git or add it as dependency to another package.

This PR adds a pyproject.toml which fixes this problem.

Additionally, it adds support for uv and a Nix dev shell.

I haven't done any README.md edits yet. Can do it if this change is welcome.

P.S. You can verify the setup is correct by following these steps:

cd <any-dir>
uv init test
cd test
uv add https://github.com/danielgafni/GazeTracking.git --branch add-packaging