Add basic Pyrefly configuration to pyproject.toml

[correctmost]

PR Description:

This makes it easier to use the Pyrefly type checker with various IDEs.

[svartkanin]

I'm not against different type checkers, but I'd be good to settle on one. Currently we're using mypy heavily, but there is ty as well (not sure how mature it is at this point). Would it make sense to evaluate them properly on the code base and stick to one?

[correctmost]

I think it's best to stick with mypy for now:

• mypy - stable and actively maintained
• Pyright - stable, but less actively maintained
• Pyrefly, ty, and zuban - still in beta

The newer type checkers have language server features, so I would expect more developers to start using them while working on archinstall. I use them with VS Code and thought it would be helpful to add configs that reduce warning noise.

I think it's okay to commit basic configs for tools like Pyright and Pyrefly to support local development, even if the tools don't end up running on CI.