Implement HyperNova's IVC into the FoldingScheme trait (#116)

- implement the IVC `FoldingScheme` trait for HyperNova
- refactor Nova's preprocess logic to make it simplier to use
- add to Decider trait (& Nova's DeciderEth) a preprocess method
- get rid of the `init_nova_ivc_params` and `init_ivc_and_decider_params` methods in `examples` since this is achieved with the `FS::preprocess` & `Decider::preprocess` methods
  - (update the examples code to the simplified interface using
    FS::preprocess & Decider::preprocess)

folding-schemes/src/commitment/pedersen.rs

@@ -38,6 +38,13 @@ impl<C: CurveGroup, const H: bool> CommitmentScheme<C, H> for Pedersen<C, H> {
     type ProverChallenge = (C::ScalarField, Vec<C::ScalarField>, C, C::ScalarField);
     type Challenge = C::ScalarField;
 
+    fn is_hiding() -> bool {
+        if H {
+            return true;
+        }
+        false
+    }
+
     fn setup(
         mut rng: impl RngCore,
         len: usize,