Support not equal operator in noname

[vuvoth]

Motivation

We should support not equal operator in noname.

assert(a != b)

Solution

[mimoo]

could be implemented as is_zero(a - b), see for example https://github.com/Consensys/gnark/blob/master/frontend/cs/r1cs/api.go#L535

[mimoo]

we might already have a == b, so checking that a - b == 0 should work