putio: handle rate limit errors

For rate limit errors, "x-ratelimit-reset" header is now respected.

backend/putio/putio.go

@@ -33,8 +33,9 @@ const (
 	rcloneObscuredClientSecret = "cMwrjWVmrHZp3gf1ZpCrlyGAmPpB-YY5BbVnO1fj-G9evcd8"
 	minSleep                   = 10 * time.Millisecond
 	maxSleep                   = 2 * time.Second
-	decayConstant              = 2 // bigger for slower decay, exponential
+	decayConstant              = 1 // bigger for slower decay, exponential
 	defaultChunkSize           = 48 * fs.Mebi
+	defaultRateLimitSleep      = 60 * time.Second
 )
 
 var (