[Bug] Users % targettig does not seem to work as one could think is does

### [REQUIRED] Please fill in the following fields:

* Pre-built SDK from the [website](https://firebase.google.com/download/cpp) or open-source from this repo: Open source from this repo
* Firebase C++ SDK version: 8.9.0
* Problematic Firebase Component: Remote config
* Other Firebase Components in use: None
* Platform you are using the C++ SDK on: Windows, Mac
* Platform you are targeting: desktop

### [REQUIRED] Please describe the issue here:

Users % targettig does not seem to work as it should. It rolls a dice every fetch so it does not have any notion of a user or client thus single client can get various configs every fetch

#### Steps to reproduce:

Configure remote config so it has a user % based condition and serve one config (config A) for 50% of users and the other (config B) for the rest. Fetch the config multiple times.
Expected: A user who got config A keeps getting config A and the one who got config B always gets config B.
Actual: The user who got config A gets config B on subsequent fetch.

#### Relevant Code:

未指定任何文件或测试。首先定位用于用户百分比条件的 C++ Remote Config 实现，并在 Windows 或 Mac 上使用 50/50 配置复现重复 fetch。完成标准是：收到配置 A 或 B 的客户端在后续 fetch 中仍持续收到相同的分配。

由索引模型根据 Issue 内容生成。