Suppress compiler noise in tests folder

By having two modules that declare and use the `harness` module we ran
into a situation where not all parts of the `harness` module were
being used by both of these other test modules. This was producing
annoying warnings.

For now this can be solved by marking the `harness` module declaration
as public. This has no real effect since modules under `/tests` cannot
be depended on elsewhere, but it satisfies the compiler. It does mean
that we will not hear about unused functions, but this change should
be temporary and it's a very minor problem given that it's just test
code.

xmr-btc/tests/e2e.rs

@@ -1,3 +1,5 @@
+pub mod harness;
+
 use crate::harness::wallet;
 use bitcoin_harness::Bitcoind;
 use harness::{
@@ -13,8 +15,6 @@ use tokio::sync::{
 };
 use xmr_btc::{alice, bitcoin, bob, monero};
 
-mod harness;
-
 const TEN_XMR: u64 = 10_000_000_000_000;
 const RELATIVE_REFUND_TIMELOCK: u32 = 1;
 const RELATIVE_PUNISH_TIMELOCK: u32 = 1;

xmr-btc/tests/on_chain.rs

@@ -1,4 +1,4 @@
-mod harness;
+pub mod harness;
 
 use anyhow::Result;
 use genawaiter::GeneratorState;