Migrate to pyproject.toml

[sharkdp]

I'm not sure if this is a desired change for this project. Please feel free to close this without comment if you think it's unnecessary. mypy_primer works fine without this.

The idea is to replace the setup.py-based configuration with a pyproject.toml file. The main motivating reasons for this PR are:

• Being able to just use uv/poetry/pdm run mypy_primer.
• To declare the development dependencies so that I can run them without having to install them locally
• Being able to run test.sh without having to install black/flake8/isort/mypy globally
• To lock the dependencies to make sure that every developer uses the same version of black/flake8/isort/mypy when working on this project

I verified that it is still possible to install mypy_primer using pip, like it's done in the mypy CI pipeline here.

Disclaimer: I work for @astral-sh. It's certainly not my goal to promote uv with this PR. I saw that mypy_primer already uses uv internally, for its testing, and in the CI pipeline. So I thought it would be fine to double-down on that decision. This PR also adds a uv.lock file to make sure everyone uses the same versions of the dev tools. I can also remove it if a tool-specific lock file (while we wait for PEP-751) is not desirable for some reason.

[hauntsaninja]

Thank you! And yeah, using uv internally made mypy_primer much faster :-)