chore: Use 7 bit rom tables in biggroup

[suyash67]

Using groups of 7 points (instead of 6) gives a slight improvement in recursive verifier circuit sizes:

Flavor	N	Before	After	% improv.	Dyadic (before)	Dyadic (after)	Boundary?
UltraRecursive	63	531,999	501,978	5.6%	2²⁰	2¹⁹	Yes
UltraZKRecursive	67	568,343	539,706	5.0%	2²⁰	2²⁰	No
MegaZKRecursive	76	645,124	598,440	7.2%	2²⁰	2²⁰	No
MegaRecursive	81	685,558	643,576	6.1%	2²⁰	2²⁰	No

This is not intended to be merged as of now, we'll revisit this.