* Fix Nova multi-elements state

In the AugmentedFCircuit the default value for the state when no input
is provided was `vec![F::zero()]`, which defaults to length `1`. So when
having more than 1 element in the state, before even starting to fold,
the circuit was already already failing.

Additionally this commit adds an example for a circuit with a state of 5
elements.

* abstract 'nova_setup' helper to avoid code duplication in examples

* update example naming to 'MultiInputs'

* rename nova_setup -> test_nova_setup to make it more explicit