- 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