Integration tests for ruff_python_ast

This crate includes integration tests for the ruff_python_ast crate.

The reason for having a separate crate is to avoid introducing a dev circular dependency between the ruff_python_parser crate and the ruff_python_ast crate.

This crate shouldn't include any code, only tests.

Reference:

• rust-analyzer issue: https://github.com/rust-lang/rust-analyzer/issues/3390
• Ruff's pull request: https://github.com/astral-sh/ruff/pull/11261