fix: memory leak when gcache.NewAdapterMemory with lru

[qinyuguang]

Example

package main

import (
	"context"
	"runtime"
	"time"

	"github.com/gogf/gf/v2/frame/g"
	"github.com/gogf/gf/v2/os/gcache"
)

func main() {
	ctx := context.Background()

	cache := gcache.NewAdapterMemory(1)
	cache.Set(ctx, "key", "value", 10*time.Minute)

	var m runtime.MemStats
	timer1 := time.NewTicker(time.Microsecond)
	timer2 := time.NewTicker(time.Second)
	var i int
	for {
		select {
		case <-timer1.C:
			i++
			cache.Get(ctx, "key")
		case <-timer2.C:
			runtime.ReadMemStats(&m)
			size, _ := cache.Size(ctx)
			g.Log().Infof(ctx, "memory usage: %dKB, gc num: %d, gcache size: %d, call times: %d", m.HeapInuse/1024, m.NumGC, size, i)
		}
	}
}                                                                                                                                               

Output