Fix timer deletion for short delays

[jeryaiwei]

Added a fix to delete timers with short delays.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[jeryaiwei]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

1. timer.item.removed = true：
   这是一个标记，用于指示任务已被逻辑删除。在 scanAndRunTasks 方法中，如果任务被标记为 removed，会从槽位列表中移除，避免重复执行。虽然在立即执行的情况下，任务没有重新插入槽位，但保留这个标记可以确保代码的一致性和健壮性，防止潜在的竞态条件或意外重复执行。
2. tw.timers.Del(task.key):
   映射中删除键，确保映射中不保留无效条目。
   如果不删除，映射中会保留指向已执行任务的引用，可能导致内存泄漏（虽然 Go 的 GC 会处理，但不利于代码清晰）。
   在后续的 SetTimer 或 MoveTimer 操作中，如果键已存在但指向无效条目，可能引发逻辑错误或不一致的行为。

func TestTimingWheel_MoveTimerImmediateExecution(t *testing.T) {
   var executionCount int32
   ticker := timex.NewFakeTicker()
   tw, _ := NewTimingWheelWithTicker(testStep, 10, func(k, v any) {
   	atomic.AddInt32(&executionCount, 1)
   	assert.Equal(t, "test_key", k)
   	assert.Equal(t, "test_value", v)
   }, ticker)
   defer tw.Stop()

   // Set initial task
   tw.SetTimer("test_key", "test_value", testStep*5)

   // Move to short delay (less than interval), should execute immediately
   tw.MoveTimer("test_key", testStep>>1)

   // Wait for a while to ensure no extra execution
   time.Sleep(waitTime)

   // Verify executed only once
   assert.Equal(t, int32(1), atomic.LoadInt32(&executionCount))

   // Verify the map has been cleaned up
   _, exists := tw.timers.Get("test_key")
   assert.False(t, exists, "The map should not retain entries for executed tasks")
}

[jeryaiwei]

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