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/build.rs

@@ -0,0 +1,67 @@
+use std::{
+  io::Write,
+  path::Path,
+  fs::{File, remove_file},
+};
+
+use dalek_ff_group::EdwardsPoint;
+
+use monero_generators::bulletproofs_generators;
+
+fn serialize(generators_string: &mut String, points: &[EdwardsPoint]) {
+  for generator in points {
+    generators_string.extend(
+      format!(
+        "
+          dalek_ff_group::EdwardsPoint(
+            curve25519_dalek::edwards::CompressedEdwardsY({:?}).decompress().unwrap()
+          ),
+        ",
+        generator.compress().to_bytes()
+      )
+      .chars(),
+    );
+  }
+}
+
+fn generators(prefix: &'static str, path: &str) {
+  let generators = bulletproofs_generators(prefix.as_bytes());
+  #[allow(non_snake_case)]
+  let mut G_str = "".to_string();
+  serialize(&mut G_str, &generators.G);
+  #[allow(non_snake_case)]
+  let mut H_str = "".to_string();
+  serialize(&mut H_str, &generators.H);
+
+  let path = Path::new(".generators").join(path);
+  let _ = remove_file(&path);
+  File::create(&path)
+    .unwrap()
+    .write_all(
+      format!(
+        "
+          lazy_static! {{
+            static ref GENERATORS: Generators = Generators {{
+              G: [
+                {}
+              ],
+              H: [
+                {}
+              ],
+            }};
+          }}
+        ",
+        G_str, H_str,
+      )
+      .as_bytes(),
+    )
+    .unwrap();
+}
+
+fn main() {
+  // For some reason, filtering off .generators does not work. This prevents re-building overall
+  println!("cargo:rerun-if-changed=build.rs");
+
+  generators("bulletproof", "generators.rs");
+  generators("bulletproof_plus", "generators_plus.rs");
+}