Arithmetic circuits support

[ArielElp]

Starknet will soon support a new builtin for evaluating arithmetic circuits in the non-native prime.

This builtin is already in use by the groth16 verifier implemented in Garaga, albeit in CairoZero.

The plan is to allow developers to build arithmetic circuits based on the language's type system. By introducing the following new types: In<N>, Add<C1,C2>, Mul<C1,C2>, developers will be able to define complex arithmetic circuits. A new ciruit_eval libfunc will be added to evaluate the circuit given the inputs.

At the Sierra level, the circuit is a large type. At the CASM level, the circuit is just a long chunk of assembly similarly to how it looks in CairoZero today. Applications of the new builtin will only happen upon usage of circuit_eval.