java cllient read data from cpp server is too slow

**Describe the bug (描述bug)**
java client 异步 rpc 从 cpp server 读取数据，每次拿一个包，带宽用不满，只有到 30% 左右，怎么提升网络利用率？

**To Reproduce (复现方法)**

StarRocks FE 从 BE 读取大结果集，比如 select * from table，当结果集很大的时候，卡在网络上

**Expected behavior (期望行为)**
用满带宽

**Versions (各种版本)**
OS:
Compiler:
brpc:
protobuf:

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

The issue names no files, tests, or entry points. Start by reproducing the Java client's asynchronous RPC reads from a C++ server with a large StarRocks FE/BE result set, then measure packet handling and bandwidth usage. Done means identifying and validating a change that substantially improves network utilization.

Written by the indexing model from the issue text.