I also upgraded the flake.nix file.
- `mkShell` now use `packages` instead of `buildInputs` (See https://discourse.nixos.org/t/difference-between-buildinputs-and-packages-in-mkshell/60598/2)
- Now using `venvShellHook` to create the Python virtual environment
- Remove useless variables
- Added `meta` attrset
- Now using `python3Packages` variables instead
- Explicitly use the `build-system` field
- Now using `substituteInPlace` within `postPatch`
- Using the `pyproject` field instead of `format`
- Removed bad pratices, etc..