Support batching of more than two columns for Starky LogUp helper columns

[hratoanina]

From a message on Discord:
We are currently only allowing constraints of degree 3 or less for computing LogUp helper columns in Starky:

plonky2/starky/src/lookup.rs

Line 655 in bf95c10

pub(crate) fn eval_helper_columns<F, FE, P, const D: usize, const D2: usize>(

We could make the code support any degree by allowing batching of more than two columns together.
(This is currently low priority for our use case.)