Support RuntimeSpec

[metascroy]

🚀 The feature, motivation and pitch

Support runtime specs in CoreML ET delegate for specifying the compute unit and reshapeFrequency at runtime.

Backend runtime configuration proposal for ET: https://docs.google.com/document/d/1a6CVvbn1-CkDhUD-MCWTEXXCNXAnfjd9BD86iKf7g2c/edit?tab=t.0

Alternatives

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Additional context

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RFC (Optional)

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