[Proposal] dubbo benchmark需完善

当前的dubbo-benchmark没有原生gRPC的案例，无法对比dubbo tri与gRPC的性能差异。
其次目前的案例中也缺少较大请求报文的案例，无法得知请求大报文时的性能表现，例如`tri`协议在请求大报文时频繁更新流控窗口的性能表现。

Start by locating the existing dubbo-benchmark scenarios and their protocol configuration. Compare how the current tri cases are structured, then determine how native gRPC and large-request cases should fit alongside them. Done means the benchmark can compare tri with gRPC and exercise performance with large request payloads, including tri flow-control behavior.

Written by the indexing model from the issue text.