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>

.ruff.toml

@@ -0,0 +1,37 @@
+# Suggested config from pytorch that we can adapt
+lint.select = ["B", "C", "E" , "F" , "N", "W", "B9"]
+
+line-length = 120
+
+# C408 ignored because we like the dict keyword argument syntax
+# E501 is not flexible enough, we're using B950 instead
+# N812 ignored because import torch.nn.functional as F is PyTorch convention
+# N817 ignored because importing using acronyms is convention (DistributedDataParallel as DDP)
+# E731 allow usage of assigning lambda expressions
+# E701 let black auto-format statements on one line
+# E704 let black auto-format statements on one line
+lint.ignore = [
+    "E203", "E305", "E402", "E501", "E721", "E741", "F405", "F821", "F841",
+    "C408", "E302", "W291", "E303", "N812", "N817", "E731", "E701",
+    # These are the additional ones we started ignoring after moving to ruff. We should look into each one of them later.
+    "C901", "C405", "C414", "N803", "N999", "C403", "C416", "B028", "C419", "C401", "B023",
+    # shebang has extra meaning in fbcode lints, so I think it's not worth trying
+    # to line this up with executable bit
+    "EXE001",
+    # random naming hints don't need
+    "N802",
+    # these ignores are from flake8-bugbear; please fix!
+    "B007", "B008"
+]
+
+exclude = [
+    "./.git",
+    "./docs/*",
+    "./build",
+    "./scripts",
+    "./venv",
+    "*.pyi",
+    ".pre-commit-config.yaml",
+    "*.md",
+    ".flake8"
+]