non-deterministic rewriter behavior in onnxscript

When running the onnxscript_bug.py multiple times on the attached input model, sometimes it will apply a rewrite rule, other times it won't. In the below text, 6 out of 20 runs triggered a rewrite. Non-deterministic behavior should be avoided at all cost, as it complicates matters. ``` $ cat onnxscript_bug.py from onnxscript import ir from onnxscript.optimizer import optimize_ir ir_model = ir.load("input.onnx") optimize_ir(ir_model, num_iterations = 1) ir.save(ir_model, "output.onnx") $ for i in {1..20}; do python onnxscript_bug.py; done Applied 1 of general pattern rewrite rules. Applied 1 of general pattern rewrite rules. Applied 1 of general pattern rewrite rules. Applied 1 of general pattern rewrite rules. Applied 1 of general pattern rewrite rules. Applied 1 of general pattern rewrite rules. $ pip list | grep onnx onnx 1.19.1 onnx-ir 0.2.0 onnxscript 0.6.2 sne4onnx 2.0.1 ``` [input.onnx.zip](https://github.com/user-attachments/files/26420676/input.onnx.zip) the resulting graphs show the difference: <img width="291" height="401" alt="Image" src="https://github.com/user-attachments/assets/bea1a70f-5e84-46e1-b77f-223e47f30cb1" /> <img width="301" height="389" alt="Image" src="https://github.com/user-attachments/assets/b5452a72-e123-4274-882d-022151a5c660" />