🤔 [QUESTION] 请问mix有多个折线图如何配置label

### 🐛 Question description [Please make everyone to understand it]
配置了`top： true`共享顶层data的mix图表给每个plot单独配置label只有最后一个图层会生效，label好像也不支持在顶层配置。
### 💻 Link to minimal reproduction
[链接](https://codesandbox.io/p/sandbox/condescending-lamport-rxrrgh?file=%2Fsrc%2FApp.js%3A133%2C19)

### 🏞 Expected result
期望每个图层的label都生效
### 🚑 Any additional [like screenshots]

* **G2Plot Version**:
* **Platform**:

Start with the linked CodeSandbox reproduction and inspect the mix chart configuration using top: true, focusing on how per-plot labels are processed. Confirm the issue when multiple line plots are configured, and consider the work complete when each plot's label takes effect rather than only the last one.

Written by the indexing model from the issue text.