fix(bugbot): simplify rate-limit label coercion + guard None detail

- prometheus.py _extract_rate_limit_labels: RateLimitError.__init__ already
  normalizes category/rate_limit_type to plain str, so the getattr(.value)
  + isinstance dance was dead code. Reduce to str(value) if not None.
- proxy_rate_limit_error.py _coerce_message: short-circuit None to ''
  instead of falling through to str(None) = 'None', which produced the
  literal message 'litellm.RateLimitError: None'.

litellm/integrations/prometheus.py

@@ -2697,12 +2697,7 @@ class PrometheusLogger(CustomLogger):
             return None, None
 
         def _coerce(value: Any) -> Optional[str]:
-            if value is None:
-                return None
-            inner = getattr(value, "value", None)
-            if isinstance(inner, str):
-                return inner
-            return str(value)
+            return str(value) if value is not None else None
 
         return (
             _coerce(getattr(exception, "category", None)),

litellm/proxy/common_utils/proxy_rate_limit_error.py

@@ -67,6 +67,8 @@ def map_v3_rate_limit_type(
 
 def _coerce_message(detail: Any) -> str:
     """Best-effort, JSON-friendly stringification of an HTTPException-style detail."""
+    if detail is None:
+        return ""
     if isinstance(detail, str):
         return detail
     if isinstance(detail, Mapping):