[CI] Enable ruff INP to require __init__.py under vllm/ (#56264)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

pyproject.toml

@@ -55,6 +55,8 @@ where = ["."]
 include = ["vllm*"]
 
 [tool.ruff.lint.per-file-ignores]
+# `vllm` is the only installed package; everything else is standalone scripts
+"!vllm/**" = ["INP"]
 "vllm/third_party/**" = ["ALL"]
 "vllm/version.py" = ["F401"]
 "vllm/_version.py" = ["ALL"]
@@ -77,6 +79,8 @@ select = [
     "I",
     # flake8-logging-format
     "G",
+    # flake8-no-pep420
+    "INP",
 ]
 ignore = [
     # star imports