pkg/escape: Preallocate output in Unescape

Preallocating the capacity of the output is faster and uses less
memory than letting append() do its own (over)allocation.

pkg/escape/bytes.go

@@ -78,7 +78,11 @@ func Unescape(in []byte) []byte {
 
 	i := 0
 	inLen := len(in)
-	var out []byte
+
+	// The output size will be no more than inLen. Preallocating the
+	// capacity of the output is faster and uses less memory than
+	// letting append() do its own (over)allocation.
+	out := make([]byte, 0, inLen)
 
 	for {
 		if i >= inLen {