feat(proxy,failover,transport): Hyper 上游客户端精细计时、连续失败退避与连接泄漏修复

Proxy:
- 将上游 HTTP 客户端从 reqwest 替换为 hyper，新增 InstrumentedConnector
  实现 TCP 连接/TLS 握手级别的独立计时，上报 connection_reused 等指标
- 前端展示细粒度代理计时（连接复用、等待响应头等）

Failover:
- 引入连续失败退避机制，每 10 次失败递增退避间隔
- 检测 H2 max outbound streams 错误并触发上游客户端重建
- 新增 HTTPClientPool.reset_upstream_client 支持按需重建缓存客户端

连接泄漏修复:
- Handler 异常路径确保 response_ctx 被正确关闭
- HubResponseStream 迭代结束后在 finally 块中清理 stream_id
- HubTunnelTransport.handle_request 捕获所有异常并清理流状态

aether-proxy/Cargo.toml

@@ -7,7 +7,11 @@ description = "Tunnel proxy for Aether"
 [dependencies]
 tokio = { version = "1", features = ["full"] }
 reqwest = { version = "0.12", default-features = false, features = ["json", "rustls-tls", "stream", "http2"] }
+hyper = { version = "1", features = ["client", "http1", "http2"] }
+hyper-util = { version = "0.1", features = ["client", "client-legacy", "http1", "http2", "tokio"] }
+http-body-util = "0.1"
 tokio-tungstenite = { version = "0.24", features = ["rustls-tls-webpki-roots"] }
+tokio-rustls = "0.26"
 futures-util = "0.3"
 base64 = "0.22"
 clap = { version = "4", features = ["derive", "env"] }
@@ -31,6 +35,7 @@ libc = "0.2"
 flate2 = "1"
 tar = "0.4"
 socket2 = { version = "0.5", features = ["all"] }
+tower-service = "0.3"
 webpki-roots = "0.26"
 
 [profile.release]