bench(jolt-sumcheck): add criterion benchmarks for verifier paths

[wstran]

Summary

jolt-sumcheck is the only modular crate with fuzz coverage but no
criterion benchmarks (the four crates already in
bench-crates.yml — jolt-crypto, jolt-field, jolt-poly,
jolt-transcript — all publish baselines). This PR adds a
benches/sumcheck_verifier.rs covering both verifier entry points and
wires the crate into the existing matrix so future regressions show up
on PR via the critcmp diff against the main baseline.

Benches

• SumcheckVerifier::verify/{8,14,18,22} — single-instance honest-proof
  verification across realistic round counts.
• BatchedSumcheckVerifier::verify/same_size/{n_vars=14,18}/{n_claims=2,4}
  — front-loaded RLC batching path.

Each bench builds an honest proof with a minimal in-bench reference
prover (mirroring the honest_prove helper from
crates/jolt-sumcheck/src/tests.rs) so the verifier exercises the
full Fiat-Shamir loop end-to-end, not just round-0 rejection.

Local numbers

apple-darwin (M1), --warm-up-time 1 --measurement-time 3 --sample-size 10:

Bench	Time (median)
SumcheckVerifier::verify/8	3.32 µs
SumcheckVerifier::verify/14	5.68 µs
SumcheckVerifier::verify/18	7.32 µs
SumcheckVerifier::verify/22	8.89 µs
BatchedSumcheckVerifier::verify/n_vars=14/n_claims=2	6.10 µs
BatchedSumcheckVerifier::verify/n_vars=14/n_claims=4	6.39 µs
BatchedSumcheckVerifier::verify/n_vars=18/n_claims=2	7.73 µs
BatchedSumcheckVerifier::verify/n_vars=18/n_claims=4	7.99 µs

CI

Adds jolt-sumcheck to both the baseline (push to main) and PR
runs in .github/workflows/bench-crates.yml, mirroring the existing
four-crate matrix.

Test plan

• cargo fmt -q
• cargo clippy -p jolt-sumcheck --all-targets -- -D warnings
• cargo clippy -p jolt-core --features host --all-targets -- -D warnings
• cargo clippy -p jolt-core --features host,zk --all-targets -- -D warnings
• cargo nextest run -p jolt-sumcheck — 42/42 pass
• cargo nextest run -p jolt-core muldiv --features host — pass
• cargo nextest run -p jolt-core muldiv --features host,zk — pass
• cargo bench -p jolt-sumcheck --bench sumcheck_verifier -- --warm-up-time 1 --measurement-time 3 --sample-size 10 — numbers above