优化: ssh-proxy russh 迁移后代码整理

- 移除未使用的 async-trait 依赖
- 添加断线重连逻辑，会话失效时自动重连
- 修复 get_or_create_session TOCTOU 竞态条件
- 日志智能分级: 慢请求告警、退出码识别
- 用 time crate 替换手写日期计算 (删除40行)
- UTF-8 安全截断修复
- 同步优化 mysql-proxy 日志模块

mysql-proxy/Cargo.toml

@@ -14,6 +14,7 @@ toml = "0.8"
 anyhow = "1"
 clap = { version = "4", features = ["derive"] }
 ureq = "2"  # CLI HTTP client (2.x has simpler API)
+time = { version = "0.3", features = ["formatting", "macros"] }
 
 [profile.release]
 opt-level = "z"