Implement multi-output autotuning in Torchinductor

[edderstack]

Add support for multi-output autotuning in Torchinductor, allowing templates and extern kernels to share the same operator contract without additional copy operations. This change includes updates to choice construction, benchmarking, and IR generation to handle multiple outputs seamlessly.

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[eellison]

@edderstack have you looked into the Subgraph Decomposition autotuning ? this can handle arbitrary, multiple operations and outputs.