Feat: combine multiple loops into one in sumcheck verifier

[kunxian-xia]

Rationale

We merge three loops into one:

1. observe_then_sample: observe the prover messages and then sample $n$ challenges; (load prover message)
2. part 1 of check_and_generate_subclaim: compute $p_i(r)$ and store it in a new array; (load prover message)
3. part 2 of check_and_generate_subclaim: assert that $p_i(r) = p_{i+1}(0) + p_{i+1}(1)$; (load prover mesage)

Note that the above three loops need to load prover message array by three times. And each load takes at least 7 cycles.
It's easy to see that we can merge them into one loop.

Performance

num_variables	max_degree	cycles
4	3	632 -> 498
5	3	774 -> 615

Cycle distribution

INFO     ┝━ ｉ [info]: ┌╴sumcheck verify
INFO     ┝━ ｉ [info]: │ ┌╴IOPVerifierState::verify_round_and_update_state
INFO     ┝━ ｉ [info]: │ │ ┌╴observe_then_sample
INFO     ┝━ ｉ [info]: │ │ └╴45 cycles
INFO     ┝━ ｉ [info]: │ │ ┌╴extrapolate_uni_poly
INFO     ┝━ ｉ [info]: │ │ └╴52 cycles
INFO     ┝━ ｉ [info]: │ │ ┌╴observe_then_sample
INFO     ┝━ ｉ [info]: │ │ └╴44 cycles
INFO     ┝━ ｉ [info]: │ │ ┌╴extrapolate_uni_poly
INFO     ┝━ ｉ [info]: │ │ └╴52 cycles
INFO     ┝━ ｉ [info]: │ │ ┌╴observe_then_sample
INFO     ┝━ ｉ [info]: │ │ └╴44 cycles
INFO     ┝━ ｉ [info]: │ │ ┌╴extrapolate_uni_poly
INFO     ┝━ ｉ [info]: │ │ └╴52 cycles
INFO     ┝━ ｉ [info]: │ │ ┌╴observe_then_sample
INFO     ┝━ ｉ [info]: │ │ └╴44 cycles
INFO     ┝━ ｉ [info]: │ │ ┌╴extrapolate_uni_poly
INFO     ┝━ ｉ [info]: │ │ └╴52 cycles
INFO     ┝━ ｉ [info]: │ └╴473 cycles
INFO     ┕━ ｉ [info]: └╴498 cycles