text: Title: FastAPI background_task cleanup is not executed upon error
  Body: FastAPI `background_task` cleanup is not executed if any error is encountered.
  
  To reproduce, run this code and add a print in cleanup function. 
  
  ```py
  import litserve as ls
  
  
  class SimpleLitAPI(ls.LitAPI):
      def setup(self, device):
          # Set up the model, so it can be called in `predict`.
          self.model = lambda x: x**2+"e"
  
      def decode_request(self, request):
          # Convert the request payload to your model input.
          return request["input"]
  
      def predict(self, x):
          # Run the model on the input and return the output.
          return self.model(x)
  
      def encode_response(self, output):
          # Convert the model output to a response payload.
          return {"output": output}
  
  ```