skip PCS of range table

[hero78119]

An follow-up enhancement after #654 , for we can skip fixed_commit & PCS of range table due to its well-form via structural_witness feature introduced in PR #740

ceno/ceno_zkvm/src/tables/range/range_impl.rs

Line 31 in 4d3948f

let fixed = cb.create_fixed(|| "fixed")?;

[hero78119]

completed via #797