Cli option for greedy relayer + run no-losses relayer by default (#1042)

* cli option for greedy relayer + run no-losses relayer by default

* trigger build

* Revert "trigger build"

This reverts commit f77ae3a634b909bb4dc915941a4c1011a86019f0.

* NoLosses -> Rational

bridges/relays/messages/src/message_lane.rs

@@ -21,7 +21,7 @@
 
 use num_traits::{SaturatingAdd, Zero};
 use relay_utils::{BlockNumberBase, HeaderId};
-use std::fmt::Debug;
+use std::{fmt::Debug, ops::Sub};
 
 /// One-way message lane.
 pub trait MessageLane: 'static + Clone + Send + Sync {
@@ -40,7 +40,15 @@ pub trait MessageLane: 'static + Clone + Send + Sync {
 	/// 1) pay transaction fees;
 	/// 2) pay message delivery and dispatch fee;
 	/// 3) pay relayer rewards.
-	type SourceChainBalance: Clone + Copy + Debug + PartialOrd + SaturatingAdd + Zero + Send + Sync;
+	type SourceChainBalance: Clone
+		+ Copy
+		+ Debug
+		+ PartialOrd
+		+ Sub<Output = Self::SourceChainBalance>
+		+ SaturatingAdd
+		+ Zero
+		+ Send
+		+ Sync;
 	/// Number of the source header.
 	type SourceHeaderNumber: BlockNumberBase;
 	/// Hash of the source header.