feat: 希望新增一个类似GetOrUpdate的方法

[JHue58]

有的时候希望在取得Value的时候，在锁持有期间内对Value进行一些判断操作然后再更新值。
现阶段只能通过Upsert()方法来实现，但是如果不进行更新时，就需要upsert相同的元素，但其实是没有必要的。

[z1324090221]

Title:
feat: Request for a method similar to GetOrUpdate

Content:
Sometimes, when retrieving a value, it is necessary to perform some judgment operations on the value while holding the lock and then update it accordingly. Currently, this can only be achieved using the Upsert() method. However, if no update is required, the same element has to be upserted again, which is unnecessary. Therefore, it would be beneficial to have a method that allows for retrieving, checking, and conditionally updating the value within the same locked operation.

[libranwmq]

You can use atomic operations to perform updates, such as atomic.CAS, and add a GetOrUpdate() method similar to the update behavior in sync.Map.