Unsupported slice indexes to iter a graph

[Johansmm]

Based on microsoft/onnxscript#2302

Code to reproduce the error:

import onnx
import onnx_ir

model = onnx.parser.parse_model(
"""<ir_version: 10, opset_import: [ "" : 17]>
     agraph (float[N] x) => (float[N] z) {
         y = Sigmoid(x)
         z = Mul(y, y)  
     }""")
ir_model = onnx_ir.from_proto(model)
ir_model.graph[0:]

Error logs

Errors when executing ir_model.graph[0:]:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "onnx_ir\_core.py", line 2232, in __getitem__
    return self._nodes[index]
           ~~~~~~~~~~~^^^^^^^
  File "onnx_ir\_linked_list.py", line 144, in __getitem__
    if index >= self._length or index < -self._length:
       ^^^^^^^^^^^^^^^^^^^^^
TypeError: '>=' not supported between instances of 'slice' and 'int'