Generate Bulletproofs(+) generators at compile time

Creates a new monero-generators crate so the monero crate can run the 
code in question at build time.

Saves several seconds from running the tests.

Closes https://github.com/serai-dex/serai/issues/101.

coins/monero/generators/src/lib.rs

@@ -0,0 +1,61 @@
+use lazy_static::lazy_static;
+
+use tiny_keccak::{Hasher, Keccak};
+
+use curve25519_dalek::{
+  constants::ED25519_BASEPOINT_POINT,
+  edwards::{EdwardsPoint as DalekPoint, CompressedEdwardsY},
+};
+
+use group::Group;
+use dalek_ff_group::EdwardsPoint;
+
+mod varint;
+use varint::write_varint;
+
+mod hash_to_point;
+pub use hash_to_point::hash_to_point;
+
+fn hash(data: &[u8]) -> [u8; 32] {
+  let mut keccak = Keccak::v256();
+  keccak.update(data);
+  let mut res = [0; 32];
+  keccak.finalize(&mut res);
+  res
+}
+
+lazy_static! {
+  pub static ref H: DalekPoint =
+    CompressedEdwardsY(hash(&ED25519_BASEPOINT_POINT.compress().to_bytes()))
+      .decompress()
+      .unwrap()
+      .mul_by_cofactor();
+}
+
+const MAX_M: usize = 16;
+const N: usize = 64;
+const MAX_MN: usize = MAX_M * N;
+
+#[allow(non_snake_case)]
+pub struct Generators {
+  pub G: [EdwardsPoint; MAX_MN],
+  pub H: [EdwardsPoint; MAX_MN],
+}
+
+pub fn bulletproofs_generators(prefix: &'static [u8]) -> Generators {
+  let mut res =
+    Generators { G: [EdwardsPoint::identity(); MAX_MN], H: [EdwardsPoint::identity(); MAX_MN] };
+  for i in 0 .. MAX_MN {
+    let i = 2 * i;
+
+    let mut even = H.compress().to_bytes().to_vec();
+    even.extend(prefix);
+    let mut odd = even.clone();
+
+    write_varint(&i.try_into().unwrap(), &mut even).unwrap();
+    write_varint(&(i + 1).try_into().unwrap(), &mut odd).unwrap();
+    res.H[i / 2] = EdwardsPoint(hash_to_point(hash(&even)));
+    res.G[i / 2] = EdwardsPoint(hash_to_point(hash(&odd)));
+  }
+  res
+}