Integrate Jagged PCS for Ceno CPU

[hero78119]

Problem

Ceno CPU needs Jagged PCS as a drop-in PCS path so per-chip commitments can be reduced into one q' opening over the existing inner PCS.

Approach

• Add Jagged PCS commit/open support around the existing PCS trait flow.

Testing

• cargo test -p mpcs jagged --quiet

Risk / Rollout

Main risk is opening-shape mismatch between padded Ceno MLEs and native q'. Rollout should stay CPU-only first; GPU integration can follow after CPU e2e validation.

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