Removed totalCostLimit from MemoryConfig

[guoyingtao]

For NSCache, I think the totalCostLimit doesn't work if you don't use setObject(_ obj: ObjectType, forKey key: KeyType, cost g: Int) and pass a cost of the object which you want to cache.

Also, I think it's not easy to get the cost of each object since they may be any type. So keeping this property may confuse user when they really try to set it.

I checked several image cache libraries based on NSCache and found they did passed the cost of the cached images because it's easy to get an image cost.

setObject function in MemoryStorage.swift

func setObject<T: Codable>(_ object: T, forKey key: String, expiry: Expiry? = nil) {
    let capsule = MemoryCapsule(value: object, expiry: .date(expiry?.date ?? config.expiry.date))
    cache.setObject(capsule, forKey: NSString(string: key))
    keys.insert(key)
}

[vadymmarkov]

Makes sense to me. What do you think @onmyway133 ?

[onmyway133]

👍