Split port traffic service and replace deprecated UTC/lifespan APIs.

Keep the public facade stable while moving device CRUD and sample/compare
logic into focused modules, and use naive UTC via timeutil plus FastAPI lifespan.

Co-authored-by: Cursor <cursoragent@cursor.com>

netx_api/timeutil.py

@@ -0,0 +1,9 @@
+"""Timezone helpers. DB columns store naive UTC; keep values naive for comparisons."""
+
+from __future__ import annotations
+
+from datetime import datetime, timezone
+
+
+def utcnow_naive() -> datetime:
+    return datetime.now(timezone.utc).replace(tzinfo=None)