Get Monero tests to pass on a brand new network

Updates decoy selection with an explicit panic, the removal of a divide 
by 0 (causing tests to fail on new chains), and a minor optimization 
when dealing with a large quantity of locked outputs.

Also increases documentation, acknowledging infinite loops and breakage 
from Monero more.

coins/monero/tests/rpc.rs

@@ -1,8 +1,39 @@
+use rand::rngs::OsRng;
+
+use curve25519_dalek::constants::ED25519_BASEPOINT_TABLE;
+
 use serde_json::json;
 
-use monero_serai::rpc::{EmptyResponse, RpcError, Rpc};
+use monero::{
+  network::Network,
+  util::{key::PublicKey, address::Address}
+};
 
-pub async fn mine_block(rpc: &Rpc, address: String) -> Result<EmptyResponse, RpcError> {
+use monero_serai::{random_scalar, rpc::{EmptyResponse, RpcError, Rpc}};
+
+pub async fn rpc() -> Rpc {
+  let rpc = Rpc::new("http://127.0.0.1:18081".to_string());
+
+  // Only run once
+  if rpc.get_height().await.unwrap() != 1 {
+    return rpc;
+  }
+
+  let addr = Address::standard(
+    Network::Mainnet,
+    PublicKey { point: (&random_scalar(&mut OsRng) * &ED25519_BASEPOINT_TABLE).compress() },
+    PublicKey { point: (&random_scalar(&mut OsRng) * &ED25519_BASEPOINT_TABLE).compress() }
+  ).to_string();
+
+  // Mine enough blocks decoy selection doesn't fail
+  for _ in 0 .. 1 {
+    mine_block(&rpc, &addr).await.unwrap();
+  }
+
+  rpc
+}
+
+pub async fn mine_block(rpc: &Rpc, address: &str) -> Result<EmptyResponse, RpcError> {
   rpc.rpc_call("json_rpc", Some(json!({
     "method": "generateblocks",
     "params": {