Make repository and project itself more friendly for future contributions

[fadedDexofan]

I want to try to implement the plan indicated in the title and prepare the repository for future contributions and possible participation in Hacktoberfest 2023.

And so here is the plan in my vision point by point:

1. Move all package and build managing to PDM. Something like done recently in Pydantic
2. Use Ruff and Black (already used) to all code-style checking, linting and formatting.
3. Add pre-commit hooks
4. Revisit type annotations with stricter and more precise mypy configuration
5. Migrate old test suites based on unittest to pytest
6. Write CONTRIBUTING.md guide to cover all these steps
7. Add hacktoberfest topic to repo 😄

[fadedDexofan]

@tobymao need your approvement

[tobymao]

I want to try to implement the plan indicated in the title and prepare the repository for future contributions and possible participation in Hacktoberfest 2023.

And so here is the plan in my vision point by point:

1. Move all package and build managing to [PDM](https://github.com/pdm-project/pdm). Something like done recently in [Pydantic](https://github.com/pydantic/pydantic/blob/main/pyproject.toml)

NO

2. Use Ruff and Black (already used) to all code-style checking, linting and formatting. YES ( remove everything else except ruff and black )
3. Add pre-commit hooks NO
4. Revisit type annotations with stricter and more precise mypy configuration YES
5. Migrate old test suites based on unittest to pytest NO
6. Write CONTRIBUTING.md guide to cover all these steps YES
7. Add hacktoberfest topic to repo 😄 NO

Happy to discuss, look forward to your PRs.