HyperNova: add multi-instances folding to AugmentedFCircuit & IVC (#119)

- Adds the logic to support multi-instances folding in HyperNova's
AugmentedFCircuit & IVC.
- Adds also methods to generate new LCCCS & CCCS instances that don't
depend on the main folding chain, to be folded in in the next step
- Updates CycleFold circuit & methods to work other folding schemes than
  Nova, adapting it to fold multiple points per circuit (instead of
2-to-1 as till now)
- Handle multi-instances folding in the FoldingScheme trait
  interface, which expects 'None' in Nova, and 'Some' in HyperNova &
other multi-folding schemes.

examples/full_flow.rs

@@ -102,7 +102,7 @@ fn main() {
     let nova_params = N::preprocess(&mut rng, &nova_preprocess_params).unwrap();
 
     // initialize the folding scheme engine, in our case we use Nova
-    let mut nova = N::init(nova_params.clone(), f_circuit, z_0).unwrap();
+    let mut nova = N::init(&nova_params, f_circuit, z_0).unwrap();
 
     // prepare the Decider prover & verifier params
     let (decider_pp, decider_vp) = D::preprocess(&mut rng, &nova_params, nova.clone()).unwrap();
@@ -110,7 +110,7 @@ fn main() {
     // run n steps of the folding iteration
     for i in 0..n_steps {
         let start = Instant::now();
-        nova.prove_step(rng, vec![]).unwrap();
+        nova.prove_step(rng, vec![], None).unwrap();
         println!("Nova::prove_step {}: {:?}", i, start.elapsed());
     }