Introduce clone model

[Johansmm]

I would like to know if it is possible to clone an ir.Model from API. I would like something like we can make in onnx:

new_model = onnx.ModelProto()
new_model.CopyFrom(original_model)

Or simpler as:

new_model_ir = original_model_ir.clone()

Today, (to make this) I have to go through onnx:

def clone_ir_model(model):
    return ir.from_proto(ir.to_proto(model))

Which is not optimal

[Johansmm]

Is this related to #58 ?

[justinchuby]

Yes. We always wanted to create a clone method but didn't get to it yet. Contribution welcome if you are interested!

[Johansmm]

@justinchuby Ok I can make this. But Should I start with previous work #96? Or maybe start from a new one?

[justinchuby]

Feel free to leverage it if you find it useful, or start from scratch at your discretion as the previous PR was copilot generated, thanks!