feat: support max running tasks config (#112)

pkg/util/timer.go

@@ -2,12 +2,17 @@ package util
 
 import "time"
 
-// 计时器
 type Timer struct {
 	t    int64
 	used int64
 }
 
+func NewTimer(used int64) *Timer {
+	return &Timer{
+		used: used,
+	}
+}
+
 func (t *Timer) Start() {
 	t.t = time.Now().UnixNano()
 }