sumcheck: convert FinalEvalProof in valueOfProof to emulated types

[sashass1315]

Description

• Implement type-switch in valueOfProof to preserve FinalEvalProof.
• Handle nil, big.Int, []big.Int, and [][]big.Int by mapping to emulated.Element[FR] forms.
• Add math/big import; no API changes.
• Backward-compatible (current claims return nil); panic on unsupported proof types to surface integration issues.

Type of change

• New feature (non-breaking change which adds functionality)

How has this been tested?

(go test ./... and ./std/recursion/sumcheck).

Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I did not modify files generated from templates
• golangci-lint does not output errors locally
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

---

Note

Map native FinalEvalProof (nil, *big.Int, []*big.Int, [][]*big.Int) to emulated elements in valueOfProof and set on Proof; add math/big import.

• sumcheck/proof.go:
  • valueOfProof: convert native FinalEvalProof to emulated forms (nil, *big.Int, []*big.Int, [][]*big.Int), panic on unsupported types.
  • Assign converted value to Proof.FinalEvalProof; keep RoundPolyEvaluations conversion unchanged.
  • Add math/big import.

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