Fixes related to infix ops PR

[voltrevo]

Add Operation::IntegerDivide

This is a bit awkward because it's currently the same as Operation::Divide. However I think it's helpful to set up this distinction so that we can treat them differently in the future. In circom Divide means division within the finite field (eg 1/2 is 3 in modulo 5, since 3*2=1 mod 5). Because the available operations depends on the MPC backend, I think we should parameterize sim-circuit over the number system, but I'll make a discussion for this elsewhere.

Discord discussion thread.

Fix input counting bug when constructing graph for Kahn's Algorithm

I was getting CircuitError::CyclicDependencyDetected for this circuit:

pragma circom 2.0.0;

template xEqX() {
    signal input x;
    signal output out;
    
    out <== x == x;
}

component main = xEqX();

(This issue came up because the test I wrote for all infix ops contained several examples like this.)

I discovered the reason for this was that a HashSet is used for the dependencies of each node. This meant that when inserting a duplicate dependency, it was ignored by the hashset but the in-degree was still incremented. Kahn's Algorithm requires that in-degree can be decremented for each edge (including multiple edges from the same input) rather than each distinct dependency.

[brech1]

This is great! Thank you