add beta buffer function

snntorch/_neurons/leakyparallel.py

@@ -145,7 +145,7 @@ def __init__(
 
         self.rnn = nn.RNN(input_size, hidden_size, num_layers=1, nonlinearity='relu', 
                           bias=bias, batch_first=False, dropout=dropout, device=device, dtype=dtype)
-
+        self._beta_buffer
         if beta is not None:
             beta = beta.clamp(0, 1) 
 
@@ -247,7 +247,12 @@ def backward(ctx, grad_output):
             return grad, None
 
 
-
+    def _beta_buffer(self, beta, learn_beta):
+        if not isinstance(beta, torch.Tensor):
+            beta = torch.as_tensor(beta)  # TODO: or .tensor() if no copy
+        if not learn_beta:
+            self.register_buffer("beta", beta)
+
     def _graded_spikes_buffer(
     self, graded_spikes_factor, learn_graded_spikes_factor
     ):