class_docstr: A general model arch for mapping from state and action to scalar values.
  
  The model arch is often used to implement the critic in actor-critic algorithms.
code: def input_prototype(self):
      # for inference: (batchsize, feature_dim)
      return (
          rlt.FeatureData(torch.randn(1, self.state_dim)),
          rlt.FeatureData(torch.randn(1, self.action_dim)),
      )
  
file_path: ReAgent/reagent/models/critic.py
imports: from typing import List
  import torch
  import torch.fx
  from reagent.core import types
  from reagent.models.base import ModelBase
  from reagent.models.fully_connected_network import FullyConnectedNetwork
label_desc: Use image node_id 2 for calling the FullyConnectedCritic obj's underlying member method code with example usage: obj.input_prototype() and returns: rlt,  rlt