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/mod.rs

@@ -18,6 +18,8 @@ pub trait CommitmentScheme<C: CurveGroup, const H: bool = false>: Clone + Debug
     type ProverChallenge: Clone + Debug;
     type Challenge: Clone + Debug;
 
+    fn is_hiding() -> bool;
+
     fn setup(
         rng: impl RngCore,
         len: usize,