使用PartitionChannel如何做WRR负载均衡

**Is your feature request related to a problem? (你需要的功能是否与某个问题有关?)**
PartitionChannel，做分库以后，我还想做分库的WRR算法负载均衡，并且权重可以动态改变。
**Describe the solution you'd like (描述你期望的解决方法)**

**Describe alternatives you've considered (描述你想到的折衷方案)**

**Additional context/screenshots (更多上下文/截图)**

Start by locating the PartitionChannel implementation and its existing load-balancing entry points. Clarify how weighted round-robin and runtime weight changes should interact with partition selection; done would require an agreed design and tests demonstrating weighted distribution and dynamic updates.

Written by the indexing model from the issue text.