ruff

a43b683d - mdtest.py: do a full mdtest run immediately when the script is executed (#17128)

mdtest.py: do a full mdtest run immediately when the script is executed (#17128) ## Summary Currently if I run `uv run crates/red_knot_python_semantic/mdtest.py` from the Ruff repo root, I get this output: ``` ~/dev/ruff (main)⚡ % uv run crates/red_knot_python_semantic/mdtest.py Ready to watch for changes... ``` ...And I then have to make some spurious whitespace changes or something to a test file in order to get the script to actually run mdtest. This PR changes mdtest.py so that it does an initial run of all mdtests when you invoke the script, and _then_ starts watching for changes in test files/Rust code.