Fix/litellm finish reason 3109

src/google/adk/models/llm_response.py

@@ -78,7 +78,11 @@ class LlmResponse(BaseModel):
   """
 
   finish_reason: Optional[types.FinishReason] = None
-  """The finish reason of the response."""
+  """The finish reason of the response.
+
+  Always a types.FinishReason enum. String values from underlying model providers
+  are mapped to corresponding enum values (with fallback to OTHER for unknown values).
+  """
 
   error_code: Optional[str] = None
   """Error code if the response is an error. Code varies by model."""