Integrate Jagged PCS into CPU prover flow

[hero78119]

Problem

Integrate Jagged PCS into the Ceno prover flow so trace commitments/openings can use Jagged over the existing Basefold PCS.

Design Rationale

Jagged PCS packs per-chip trace polynomials into q' and reduces batched openings before delegating the final PCS opening to Basefold. The verifier behavior is kept unchanged; prover-side q' opening now reuses inner PCS column MLEs instead of rebuilding a second flat q' buffer.

Change Highlights

• ceno_zkvm: wire Jagged PCS into the CPU proving flow.
• mpcs: implement Jagged PCS trait integration and q' indexed view for opening.
• mpcs: document Basefold prover param sizing and q' layout assumptions.

Benchmark / Performance Impact

CPU shard0 benchmark is close to baseline.

GPU

Block: 23817600, GPU, CENO_GPU_CACHE_LEVEL=1, reshape height: 24

Metric	Basefold baseline	Jagged PCS	Delta	Delta %
E2E total	91.800s	83.600s	-8.200s	-8.9%
Emulator	10.200s	10.100s	-0.100s	-1.0%
App prove	76.500s	68.600s	-7.900s	-10.3%
App verify	4.020s	3.590s	-0.430s	-10.7%
commit_traces	6.857s	17.620s	+10.763s	+157.0%
extract_witness_mles	3.739s	0.004s	-3.735s	-99.9%
build_tower_witness_gpu	0.323s	1.428s	+1.105s	+342.1%
prove_tower_relation_gpu	24.857s	22.566s	-2.291s	-9.2%
prove_batched_main_constraints	15.457s	7.646s	-7.811s	-50.5%
pcs_opening	15.175s	10.083s	-5.092s	-33.6%

Shard count: 15 -> 14 (-1 shard) on block 23817600.

Source runs:

• Basefold baseline: https://github.com/scroll-tech/ceno-reth-benchmark/actions/runs/25655529702
• Jagged PCS: https://github.com/scroll-tech/ceno-reth-benchmark/actions/runs/25921358391
• Baseline summary: https://github.com/scroll-tech/ceno-reth-benchmark/blob/gh-pages/benchmarks-dispatch/refs/heads/feat/batch_main_sumcheck/mainnet23817600-20260511-150859_summary.md
• Jagged PCS summary: https://github.com/scroll-tech/ceno-reth-benchmark/blob/gh-pages/benchmarks-dispatch/refs/heads/feat/jagged_pcs/mainnet23817600-20260515-215037_summary.md

Testing

cargo test -p mpcs jagged -- --nocapture
cargo run --config net.git-fetch-with-cli=true --release --package ceno_zkvm --bin e2e -- \
  --platform=ceno --max-cycle-per-shard=1600 \
  examples/target/riscv32im-ceno-zkvm-elf/release/examples/keccak_syscall

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