use Unix Nano timestamp for "now" in poolCommon

The pool’s ticktock goroutine was storing time.Now() in an atomic.Value,
which incurs interface boxing and shows up as runtime.convT in profiles.
Switch to storing Unix nanos in an int64 with atomic.Load/StoreInt64,
and reconstruct time.Time in nowTime(). This preserves behavior while
removing the per‑tick allocation and conversion overhead, especially
when many pools are created.

Author: trace-andreason

ants.go

@@ -191,7 +191,7 @@ type poolCommon struct {
 	ticktockCtx  context.Context
 	stopTicktock context.CancelFunc
 
-	now atomic.Value
+	nowNano int64
 
 	options *Options
 }
@@ -303,7 +303,7 @@ func (p *poolCommon) ticktock() {
 			break
 		}
 
-		p.now.Store(time.Now())
+		atomic.StoreInt64(&p.nowNano, time.Now().UnixNano())
 	}
 }
 
@@ -318,13 +318,13 @@ func (p *poolCommon) goPurge() {
 }
 
 func (p *poolCommon) goTicktock() {
-	p.now.Store(time.Now())
+	atomic.StoreInt64(&p.nowNano, time.Now().UnixNano())
 	p.ticktockCtx, p.stopTicktock = context.WithCancel(context.Background())
 	go p.ticktock()
 }
 
 func (p *poolCommon) nowTime() time.Time {
-	return p.now.Load().(time.Time)
+	return time.Unix(0, atomic.LoadInt64(&p.nowNano))
 }
 
 // Running returns the number of workers currently running.