Fix precommit check after moving to ruff (#927)

Lint check in main branch is failing. This fixes the lint check after we
moved to ruff in https://github.com/meta-llama/llama-stack/pull/921. We
need to move to a `ruff.toml` file as well as fixing and ignoring some
additional checks.

Signed-off-by: Yuan Tang <terrytangyuan@gmail.com>

llama_stack/providers/tests/safety/test_safety.py

@@ -34,9 +34,7 @@ class TestSafety:
         response = await safety_impl.run_shield(
             shield_id=shield.identifier,
             messages=[
-                UserMessage(
-                    content="hello world, write me a 2 sentence poem about the moon"
-                ),
+                UserMessage(content="hello world, write me a 2 sentence poem about the moon"),
             ],
         )
         assert response.violation is None