message: [fx2trt] remove use of t.protocol
  Summary:
  Pull Request resolved:
  protocol is only in typing module after python 3.8 and we would want the minimum version requirement to be 3.7 (align with PyTorch and TensorRT).
diff: @@ -135,7 +135,7 @@ class CallableObservers:
  post: Observer[t.Callable[[ObserveContext], None]]
  -class ObservedCallable(t.Protocol):
  +class ObservedCallable:
  """
  Interface for an observed callable
  """
  