Add unit tests for remove_inputs in InputObserver

[Copilot]

remove_inputs was added to InputObserver, InputObserverInfo, and InputCandidate but had no test coverage.

Changes

• test_remove_inputs_kwargs: Verifies removing a single kwarg ("z") propagates correctly through infer_dynamic_shapes() and infer_arguments().
• test_remove_inputs_multiple_kwargs: Verifies removing multiple kwargs ("z", "w") at once leaves remaining inputs ("x", "y") intact and correctly shaped.

observer = InputObserver()
with observer(model):
    for kwargs in inputs:
        model(**kwargs)  # model(x, y, z=None, w=None)

observer.remove_inputs(["z", "w"])

ds = observer.infer_dynamic_shapes()
# {"x": {0: DYNAMIC, 1: DYNAMIC}, "y": {1: DYNAMIC}}  — z and w absent

args = observer.infer_arguments()
# {"x": tensor(...), "y": tensor(...)}  — z and w absent

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