perf: Speedup coins.Sort() when coins is of length 1

Coins.Sort() performs a heap allocation, even though sort.Sort() is in place.

This is because the compiler is doing {something} called runtime.convTSlice which internally makes a copy of the entire slice.

We should ideally find a solution that avoids this malloc for every Coins.Sort() of all sizes, but just eliminating it for slices of length <= 1 is already a big win, as Sort's are used throughout the Add and Sub logic.

types/coin.go

@@ -823,7 +823,12 @@ var _ sort.Interface = Coins{}
 
 // Sort is a helper function to sort the set of coins in-place
 func (coins Coins) Sort() Coins {
-	sort.Sort(coins)
+	// sort.Sort(coins) does a costly runtime copy as part of `runtime.convTSlice`
+	// So we avoid this heap allocation if len(coins) <= 1. In the future, we should hopefully find
+	// a strategy to always avoid this.
+	if len(coins) > 1 {
+		sort.Sort(coins)
+	}
 	return coins
 }