Test that SNARK circuits degree are unchanged

[jpraynaud]

Why

We want to make sure we detect early if a modification to the circuits changes the degree of the circuit: going to the next power of 2 would double the time to create a proof and the memory usage.

What

Add golden tests that verifies the degree of the circuits is unchanged.

How

• Add a unit test that checks the power of 2 of the number of constraints is unchanged (accessible here):
  • In the non recursive circuit (expected degree 22 in production, maybe a lower value if we compute with a lower value of k):
    • For a low value of k always (find k close to the next degree)
    • By reading the information of the golden verification key which is hardcoded
  • In the recursive circuit (expected degree 19)
• Update the run book