Optimize dense q1 row dot products

[Kuhai9801]

🚀 What’s this PR do?

Refs #134.

This replaces #201. That PR only helped the Boolean/one-hot equality-table case, while the normal PCS path uses transcript-random dense q_1.

This PR optimizes the prover-side b_j = <poly_comb_r[j], q_1> computation in ZipPlus::prove_f for dense q_1. It prepares q_1 once in Montgomery form and avoids the full field conversion for every CombR coefficient, while preserving the existing field-lift result and transcript layout.

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📎 Related issues

Refs #134

🧠 Context

The scope is the prover prove_f row-dot-product hotspot from #134. This does not claim to optimize the verifier TODO path.

Benchmarked in Codespace on AMD EPYC 7763, rustc 1.96.0, base 4454d6c.

Benchmark	Base	Head	Change
RAA BPoly<63> batch 1 2^16	33.650 ms	22.667 ms	-32.64%
RAA BPoly<63> batch 2 2^16	67.430 ms	45.548 ms	-32.45%
RAA BPoly<63> batch 5 2^16	173.300 ms	117.600 ms	-32.14%
IPRS BPoly<63> batch 1 2^13	4.5424 ms	3.4673 ms	-23.67%

✅ Checklist

• I’ve tested this locally
• I’ve added relevant docs or comments
• I’ve updated or created tests if needed
• The branch with the feature is named feature/<name>