Reduce the number of constraints in DeciderEthCircuit (#88)

* Add a dedicated variant of `mat_vec_mul_sparse` for `NonNativeFieldVar`

* Switch to a customized in-circuit nonnative implementation for efficiency

* Comments and tests for `NonNativeUintVar`

* Make `CycleFoldCircuit` a bit smaller

* Faster trusted setup and proof generation by avoiding some nested LCs

* Check the remaining limbs in a more safe way

* Format

* Disable the non-native checks in tests again

* Clarify the group operation in `enforce_equal_unaligned`

* Explain the rationale behind non-native mat-vec multiplication

* Explain the difference with some other impls of `enforce_equal_unaligned`

* Format

folding-schemes/src/folding/nova/decider_eth.rs

@@ -13,7 +13,7 @@ use super::{circuits::CF2, nifs::NIFS, CommittedInstance, Nova};
 use crate::commitment::{
     kzg::Proof as KZGProof, pedersen::Params as PedersenParams, CommitmentScheme,
 };
-use crate::folding::circuits::nonnative::NonNativeAffineVar;
+use crate::folding::circuits::nonnative::affine::NonNativeAffineVar;
 use crate::frontend::FCircuit;
 use crate::Error;
 use crate::{Decider as DeciderTrait, FoldingScheme};