Databus relation correctness

[ledwards2225]

The databus relations (which use log-derivative lookups) need to be scrutinized for correctness. Some potential issues include:

1. read_counts and read_tags must be connected. The former is boolean and takes 1 if read_counts > 0 and 0 otherwise. However this is not constrained in the relation itself.
2. Boolean values must be constrained to be boolean (e.g. read_tags), e.g. via $b^2 - b = 0$

Note: currently read_tags/counts are both treated as witnesses but I think they should actually be treated as precomputed polynomials, i.e. their values are fixed for a given circuit. This probably makes it unnecessary to perform boolean checks but may still require an established connection between read_counts and tags.