ciflow/b200/194364: Inductor: fix NVGEMM EFC reduction fallback

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Cutlass Operators 0.2 moved the shared EFC module, so import it independently from the optional dense EFC class. Preserve the identity finalizer needed by generated reductions. Direct EFC supports one generated reduction. Defer only selected composite reduction plans, which otherwise produce invalid results, and validate the regular NVGEMM fallback. Update tests to assert supported behavior rather than unsupported o…

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