Fix model inference issue with Barracuda v1.2.1 (#4766)

Co-authored-by: Ervin T. <ervin@unity3d.com>

ml-agents/mlagents/trainers/torch/distributions.py

             log_sigma = torch.clamp(self.log_sigma(inputs), min=-20, max=2)
         else:
             # Expand so that entropy matches batch size. Note that we're using
-            # torch.cat here instead of torch.expand() becuase it is not supported in the
-            # verified version of Barracuda (1.0.2).
-            log_sigma = torch.cat([self.log_sigma] * inputs.shape[0], axis=0)
+            # mu*0 here to get the batch size implicitly since Barracuda 1.2.1
+            # throws error on runtime broadcasting due to unknown reason. We
+            # use this to replace torch.expand() becuase it is not supported in
+            # the verified version of Barracuda (1.0.X).
+            log_sigma = mu * 0 + self.log_sigma
         if self.tanh_squash:
             return TanhGaussianDistInstance(mu, torch.exp(log_sigma))
         else:

ml-agents/mlagents/trainers/torch/networks.py

     ):
         super().__init__()
         self.action_spec = action_spec
-        self.version_number = torch.nn.Parameter(torch.Tensor([2.0]))
+        self.version_number = torch.nn.Parameter(
+            torch.Tensor([2.0]), requires_grad=False
+        )
-            torch.Tensor([int(self.action_spec.is_continuous())])
+            torch.Tensor([int(self.action_spec.is_continuous())]), requires_grad=False
         )
         self.continuous_act_size_vector = torch.nn.Parameter(
             torch.Tensor([int(self.action_spec.continuous_size)]), requires_grad=False
             self.encoding_size = network_settings.memory.memory_size // 2
         else:
             self.encoding_size = network_settings.hidden_units
+        self.memory_size_vector = torch.nn.Parameter(
+            torch.Tensor([int(self.network_body.memory_size)]), requires_grad=False
+        )
 
         self.action_model = ActionModel(
             self.encoding_size,
             disc_action_out,
             action_out_deprecated,
         ) = self.action_model.get_action_out(encoding, masks)
-        export_out = [
-            self.version_number,
-            torch.Tensor([self.network_body.memory_size]),
-        ]
+        export_out = [self.version_number, self.memory_size_vector]
         if self.action_spec.continuous_size > 0:
             export_out += [cont_action_out, self.continuous_act_size_vector]
         if self.action_spec.discrete_size > 0: