Smash the singular Ciphersuite trait into multiple

This helps identify where the various functionalities are used, or rather, not
used. The `Ciphersuite` trait present in `patches/ciphersuite`, facilitating
the entire FCMP++ tree, only requires the markers _and_ canonical point
decoding. I've opened a PR to upstream such a trait into `group`
(https://github.com/zkcrypto/group/pull/68).

`WrappedGroup` is still justified for as long as `Group::generator` exists.
Moving `::generator()` to its own trait, on an independent structure (upstream)
would be massively appreciated. @tarcieri also wanted to update from
`fn generator()` to `const GENERATOR`, which would encourage further discussion
on https://github.com/zkcrypto/group/issues/32 and
https://github.com/zkcrypto/group/issues/45, which have been stagnant.

The `Id` trait is occasionally used yet really should be first off the chopping
block.

Finally, `WithPreferredHash` is only actually used around a third of the time,
which more than justifies it being a separate trait.

---

Updates `dalek_ff_group::Scalar` to directly re-export
`curve25519_dalek::Scalar`, as without issue. `dalek_ff_group::RistrettoPoint`
also could be replaced with an export of `curve25519_dalek::RistrettoPoint`,
yet the coordinator relies on how we implemented `Hash` on it for the hell of
it so it isn't worth it at this time. `dalek_ff_group::EdwardsPoint` can't be
replaced for an re-export of `curve25519_dalek::SubgroupPoint` as it doesn't
implement `zeroize`, `subtle` traits within a released, non-yanked version.
Relevance to https://github.com/serai-dex/serai/issues/201 and
https://github.com/dalek-cryptography/curve25519-dalek/issues/811#issuecomment-3247732746.

Also updates the `Ristretto` ciphersuite to prefer `Blake2b-512` over
`SHA2-512`. In order to maintain compliance with FROST's IETF standard,
`modular-frost` defines its own ciphersuite for Ristretto which still uses
`SHA2-512`.

crypto/ed448/src/ciphersuite.rs

@@ -1,4 +1,4 @@
-use zeroize::Zeroize;
+use prime_field::subtle::CtOption;
 
 use sha3::{
   digest::{
@@ -8,9 +8,9 @@ use sha3::{
   Shake256,
 };
 
-use ciphersuite::{group::Group, Ciphersuite};
+use ciphersuite::{group::GroupEncoding, Id, WithPreferredHash, GroupCanonicalEncoding};
 
-use crate::{Scalar, Point};
+use crate::Point;
 
 /// Shake256, fixed to a 114-byte output, as used by Ed448.
 #[derive(Clone, Default)]
@@ -49,21 +49,14 @@ impl FixedOutput for Shake256_114 {
 }
 impl HashMarker for Shake256_114 {}
 
-#[derive(Clone, Copy, PartialEq, Eq, Debug, Zeroize)]
-pub struct Ed448;
-impl Ciphersuite for Ed448 {
-  type F = Scalar;
-  type G = Point;
+impl Id for Point {
+  const ID: &[u8] = b"ed448";
+}
+impl WithPreferredHash for Point {
   type H = Shake256_114;
-
-  const ID: &'static [u8] = b"ed448";
-
-  fn generator() -> Self::G {
-    Point::generator()
+}
+impl GroupCanonicalEncoding for Point {
+  fn from_canonical_bytes(bytes: &<Self::G as GroupEncoding>::Repr) -> CtOption<Self::G> {
+    Self::G::from_bytes(bytes)
   }
 }
-
-#[test]
-fn test_ed448() {
-  ff_group_tests::group::test_prime_group_bits::<_, Point>(&mut rand_core::OsRng);
-}

crypto/ed448/src/lib.rs

@@ -29,7 +29,6 @@ mod point;
 pub use point::Point;
 
 mod ciphersuite;
-pub use crate::ciphersuite::Ed448;
 
 pub(crate) fn u8_from_bool(bit_ref: &mut bool) -> u8 {
   use core::hint::black_box;