fix type derivation of kernel buffers

pynestml/utils/ast_utils.py

@@ -1629,6 +1629,9 @@ def create_initial_values_for_kernels(cls, neuron: ASTNeuron, solver_dicts: List
  spike_in_port = ASTUtils.get_input_port_by_name(neuron.get_input_blocks(), spike_in_port_name)
  if spike_in_port:
  type_str = NESTMLPrinter().print_data_type(spike_in_port.data_type)
+ differential_order: int = len(re.findall("__d", var_name))
+ if differential_order:
+ type_str += "*s**-" + str(differential_order)
  else:
  type_str = "real"
  expr = "0 " + type_str # for kernels, "initial value" returned by ode-toolbox is actually the increment value; the actual initial value is assumed to be 0