Simplify workers and fix metrics

internal/contract/error.go

@@ -10,3 +10,11 @@ type JobNotFoundError struct {
 func (e *JobNotFoundError) Error() string {
 	return fmt.Sprintf("%s - %s", e.State, e.Message)
 }
+
+type NoopJobError struct {
+	State string
+}
+
+func (e *NoopJobError) Error() string {
+	return fmt.Sprintf("%s: no op job occur", e.State)
+}