[LUR-11] Use expect_test in tests checking the number of constraints / variables in circuit

[huitseeker]

I would also be open to doing this for constraint and variable counts in circuits, as long as we have the appropriate guardrails and continue to orient to those as values whose changes should only be intentional and noted with close attention.

Originally posted by @porcuquine in #974 (review)

expect_test

_LUR-11