bv_utilst::equal: stop early when the result will be false

There is no need to create any further bit-level equalities when the
result will be false anyway. On aws-c-common/aws_hash_iter_next, this
reduces the number of Boolean variables from 2291304 to 584628, and the
time spent in CaDiCaL from 191 seconds to 22 seconds.

bv_utilst::equal: stop early when the result will be false

There is no need to create any further bit-level equalities when the
result will be false anyway. On aws-c-common/aws_hash_iter_next, this
reduces the number of Boolean variables from 2291304 to 584628, and the
time spent in CaDiCaL from 191 seconds to 22 seconds.