Cleanup Ruff's CLI tests

[MichaReiser]

Ruff's CLI integration tests (crates/ruff/tests) contain a lot of shared boilerplate code (shared between test functions but also test files). We should try to extract those into a more reusable testing infra. I think ty's CLI test infra works pretty well and we should try if we can use the same structure for ruff.

ruff/crates/ty/tests/cli/main.rs

Line 600 in 1f27d53

pub(crate) struct CliTest {

[Renkai]

Hi, I tried to help on this with PR:#20689
Not sure if it's the right direction. If I get yes I will keep working until the file lint.rs are all rewritten in the new style.