feat(proxy-tunnel): 实现隧道连接池与 TCP 底层优化

Rust 端:
- 支持每个 server 多条并行 WebSocket 连接 (tunnel_connections 配置)
- 手动控制 TCP 连接: connect/handshake 超时、keepalive、NODELAY (socket2)
- 预构建共享 TLS ClientConfig 避免每次重连重新解析根证书
- 增加 stale timeout 检测无数据连接，智能 backoff 按连接存活时长重置
- 每条连接独立 reconnect 计数器，仅主连接 (conn_idx=0) 发送心跳
- dispatcher 的错误帧和 PONG 改用 try_send 避免阻塞读循环
- stream_handler 增加 frame 发送超时保护防止写阻塞

Python 端:
- TunnelManager 改为连接池，按 least-loaded 策略分配请求
- handle_incoming_frame 按连接实例路由，unregister 精确移除单条连接
- 心跳和 PONG 回复改为 fire-and-forget 避免阻塞主读循环
- send_frame 增加超时保护防止 TCP 写阻塞级联
- WebSocket 先 accept 再认证，auth 加超时
- 调整 idle timeout (90s) 和 ping 间隔 (15s)

aether-proxy/Cargo.lock

@@ -27,6 +27,7 @@ dependencies = [
  "serde",
  "serde_json",
  "sha2",
+ "socket2 0.5.10",
  "sysinfo",
  "tar",
  "thiserror 2.0.18",
@@ -36,6 +37,7 @@ dependencies = [
  "tracing",
  "tracing-subscriber",
  "url",
+ "webpki-roots 0.26.11",
 ]
 
 [[package]]
@@ -907,7 +909,7 @@ dependencies = [
  "libc",
  "percent-encoding",
  "pin-project-lite",
- "socket2",
+ "socket2 0.6.2",
  "tokio",
  "tower-service",
  "tracing",
@@ -1566,7 +1568,7 @@ dependencies = [
  "quinn-udp",
  "rustc-hash",
  "rustls",
- "socket2",
+ "socket2 0.6.2",
  "thiserror 2.0.18",
  "tokio",
  "tracing",
@@ -1603,7 +1605,7 @@ dependencies = [
  "cfg_aliases",
  "libc",
  "once_cell",
- "socket2",
+ "socket2 0.6.2",
  "tracing",
  "windows-sys 0.60.2",
 ]
@@ -2149,6 +2151,16 @@ version = "1.15.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "67b1b7a3b5fe4f1376887184045fcf45c69e92af734b7aaddc05fb777b6fbd03"
 
+[[package]]
+name = "socket2"
+version = "0.5.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e22376abed350d73dd1cd119b57ffccad95b4e585a7cda43e286245ce23c0678"
+dependencies = [
+ "libc",
+ "windows-sys 0.52.0",
+]
+
 [[package]]
 name = "socket2"
 version = "0.6.2"
@@ -2441,7 +2453,7 @@ dependencies = [
  "parking_lot",
  "pin-project-lite",
  "signal-hook-registry",
- "socket2",
+ "socket2 0.6.2",
  "tokio-macros",
  "windows-sys 0.61.2",
 ]