* Port HyperNova's multifolding from https://github.com/privacy-scaling-explorations/multifolding-poc adapting and refactoring some of its methods and structs.

Note: adapted mle.rs methods from dense to sparse repr.

Co-authored-by: George Kadianakis <desnacked@riseup.net>

* HyperNova: move CCS struct outside of LCCCS & CCCS

HyperNova nimfs: move CCS structure outside of LCCCS & CCCS, to avoid
carrying around the whole CCS and duplicating data when is not needed.

Also add feature flags for the folding schemes.

---------

Co-authored-by: George Kadianakis <desnacked@riseup.net>

- Add naive decider circuit `RelaxedR1CSGadget`, which in-circuit checks
  that the given z satisfies the given RelaxedR1CS instance
- Add method to relax the R1CS instance
- Add check_relation (for testing only) to R1CS & RelaxedR1CS
- Migrate from own SparseMatrix to use ark_relations::r1cs::Matrix
- Add frontend helper to use arkworks circuits

* Implement Nova's NIFS.Verify circuits (with CycleFold)

- Add circuit for NIFS.Verify on the main curve to check the folded `u`
  & `x`
- Add circuit for NIFS.Verify on the CycleFold's auxiliary curve to
  check the folded `cm(E)` & `cm(W)`
- Add transcript.get_challenge_nbits
- Add tests for utils::vec.rs

* replace bls12-377 & bw6-761 by pallas & vesta curves (only affects tests)

We will use pallas & vesta curves (for tests only, the non-tests code
uses generics) for the logic that does not require pairings, and while
Grumpkin is not available
(https://github.com/privacy-scaling-explorations/folding-schemes/issues/12).

* update links to papers to markdown style

- port initial CCS structure with methods from multifolding-poc
- add R1CS helper methods, which will be used in Nova impl