refactor(proxy): 将 proxy resolver 同步阻塞操作异步化，避免阻塞事件循环

- 为 resolve_proxy_info、resolve_delegate_config、build_proxy_url、
  get_system_proxy_config、build_post_kwargs、build_stream_kwargs 新增
  _async 异步版本，通过 asyncio.to_thread 在工作线程中执行同步 DB 查询
- 为 _proxy_node_cache 和 _system_proxy_cache 添加 threading.Lock 保护
  多线程并发读写安全
- 大 payload 的 gzip 压缩超过 64KB 阈值时走线程池，小 payload 仍在事件
  循环中同步执行以避免不必要的线程调度开销
- hub_transport 的 frame 压缩同样增加异步版本
- 删除已无调用者的同步方法 create_client_with_proxy，将其逻辑内联至
  get_upstream_client 并改为异步
- 更新所有 handler/executor/failover 调用点使用新的异步 API
- 补充 async 版本的单元测试

tests/unit/test_proxy_resolver_compression.py

@@ -3,7 +3,15 @@ from __future__ import annotations
 import gzip
 import json
 
-from src.services.proxy_node.resolver import build_post_kwargs, build_stream_kwargs
+import pytest
+
+from src.services.proxy_node.resolver import (
+    build_post_kwargs,
+    build_post_kwargs_async,
+    build_stream_kwargs,
+    build_stream_kwargs_async,
+    resolve_proxy_info_async,
+)
 
 
 class TestProxyResolverCompression:
@@ -46,3 +54,46 @@ class TestProxyResolverCompression:
         )
 
         assert all(key.lower() != "content-encoding" for key in kwargs["headers"])
+
+    @pytest.mark.asyncio
+    async def test_build_post_kwargs_async_compresses_when_client_sent_gzip(self) -> None:
+        payload = {"message": "hello", "tokens": [1, 2, 3]}
+
+        kwargs = await build_post_kwargs_async(
+            None,
+            url="https://example.com/v1/messages",
+            headers={"Content-Type": "application/json"},
+            payload=payload,
+            timeout=10.0,
+            client_content_encoding="gzip",
+        )
+
+        assert kwargs["headers"]["Content-Encoding"] == "gzip"
+        assert json.loads(gzip.decompress(kwargs["content"]).decode("utf-8")) == payload
+
+    @pytest.mark.asyncio
+    async def test_build_stream_kwargs_async_drops_stale_content_encoding_header(self) -> None:
+        kwargs = await build_stream_kwargs_async(
+            None,
+            url="https://example.com/v1/messages",
+            headers={"content-encoding": "gzip", "Content-Type": "application/json"},
+            payload={"message": "no-gzip"},
+            timeout=10.0,
+            client_content_encoding=None,
+        )
+
+        assert all(key.lower() != "content-encoding" for key in kwargs["headers"])
+
+    @pytest.mark.asyncio
+    async def test_resolve_proxy_info_async_masks_manual_proxy_url(self) -> None:
+        info = await resolve_proxy_info_async(
+            {
+                "enabled": True,
+                "url": "socks5://user:pass@proxy.example.com:1080",
+            }
+        )
+
+        assert info == {
+            "url": "socks5://proxy.example.com:1080",
+            "source": "provider",
+        }