fix(http): 用urllib3替代requests修复SSL EOF错误

问题根因：
- Python OpenSSL 3.5.4 + requests 2.32.4 + urllib3 2.5.0 版本不兼容
- requests 2.32.4 内部使用 urllib3 的方式与 urllib3 2.5.0 API 不兼容
- curl（SecureTransport）正常工作，但 Python requests（OpenSSL）失败
- 服务器（Caddy）使用 TLS 1.3 + X25519MLKEM768（后量子密钥交换）

修复方案：
- 用 urllib3.PoolManager 直接发起 HTTP 请求（已验证可正常工作）
- 封装 _http_get() 函数替代 requests.get()
- 替换所有 requests 相关异常类型为 urllib3 异常

修改文件：
- datasource/flask_api_source.py: 核心数据源层
- rotation/simple_rotation.py: 简单轮动策略层

rotation/simple_rotation.py

@@ -14,7 +14,8 @@ import sys
 import math
 import json
 import time
-import requests
+import urllib3
+import urllib.parse
 import numpy as np
 import pandas as pd
 from pathlib import Path
@@ -26,6 +27,30 @@ sys.path.insert(0, str(PROJECT_ROOT))
 
 from rotation.config_loader import load_rotation_config, RotationStrategyConfig
 
+# ============================================================
+# HTTP client (urllib3 替代 requests，修复 SSL EOF 问题)
+# ============================================================
+
+_http_pool = urllib3.PoolManager(timeout=urllib3.Timeout(connect=10, read=120))
+
+class _HttpResponse:
+    """urllib3 响应包装，提供 requests 兼容接口"""
+    def __init__(self, resp):
+        self.status_code = resp.status
+        self._data = resp.data
+        self._json = None
+    def json(self):
+        if self._json is None:
+            self._json = json.loads(self._data)
+        return self._json
+
+def _http_get(url: str, params: dict = None, timeout: int = 120) -> _HttpResponse:
+    """使用 urllib3 发起 GET 请求（替代 requests.get，修复 OpenSSL 3.5 + Caddy 的 SSL EOF 问题）"""
+    if params:
+        url = url + '?' + urllib.parse.urlencode(params)
+    resp = _http_pool.request('GET', url, timeout=urllib3.Timeout(connect=10, read=timeout))
+    return _HttpResponse(resp)
+
 
 # ============================================================
 # Pure functions: momentum
@@ -122,7 +147,7 @@ class DataCache:
         params = {'code': code, 'start': start_date, 'end': end_date, 'adj': adj}
         for attempt in range(3):
             try:
-                resp = requests.get(url, params=params, timeout=self.timeout)
+                resp = _http_get(url, params=params, timeout=self.timeout)
                 if resp.status_code != 200:
                     if attempt < 2:
                         time.sleep(1)
@@ -149,10 +174,12 @@ class DataCache:
                     self._save_premium_cache(code, df.attrs['premium_series'])
                 print(f"  + {code}: {len(df)} rows ({adj})")
                 return df
-            except requests.exceptions.Timeout:
+            except (urllib3.exceptions.TimeoutError, urllib3.exceptions.SSLError, urllib3.exceptions.MaxRetryError, urllib3.exceptions.ProtocolError) as e:
+                # 网络相关错误（超时、SSL、连接断开）都进行重试
                 if attempt < 2:
+                    time.sleep(1 + attempt)  # 递增延迟: 1s, 2s
                     continue
-                print(f"  x {code}: timeout")
+                print(f"  x {code}: {type(e).__name__} after {attempt+1} retries")
                 return None
             except Exception as e:
                 print(f"  x {code}: {e}")
@@ -207,10 +234,10 @@ class DataCache:
         params = {'code': code, 'start': start_date, 'end': end_date, 'adj': 'raw'}
         for attempt in range(3):
             try:
-                resp = requests.get(url, params=params, timeout=self.timeout)
+                resp = _http_get(url, params=params, timeout=self.timeout)
                 if resp.status_code != 200:
                     if attempt < 2:
-                        time.sleep(1)
+                        time.sleep(1 + attempt)
                         continue
                     return
                 data = resp.json()
@@ -225,8 +252,9 @@ class DataCache:
                     self._save_premium_cache(code, self.premium_data[code])
                     print(f"  + premium {code}: +{len(new_data)} days (total {len(self.premium_data[code])})")
                 return
-            except requests.exceptions.Timeout:
+            except (urllib3.exceptions.TimeoutError, urllib3.exceptions.SSLError, urllib3.exceptions.MaxRetryError, urllib3.exceptions.ProtocolError):
                 if attempt < 2:
+                    time.sleep(1 + attempt)
                     continue
                 return
             except Exception:
@@ -238,9 +266,10 @@ class DataCache:
         params = {'market': market, 'start': start_date, 'end': end_date}
         for attempt in range(3):
             try:
-                resp = requests.get(url, params=params, timeout=self.timeout)
+                resp = _http_get(url, params=params, timeout=self.timeout)
                 if resp.status_code != 200:
                     if attempt < 2:
+                        time.sleep(1 + attempt)
                         continue
                     return None
                 data = resp.json()
@@ -253,8 +282,15 @@ class DataCache:
                 result = pd.DatetimeIndex(dates)
                 print(f"  + {market}: {len(result)} trading days ({start_date} ~ {end_date})")
                 return result
+            except (urllib3.exceptions.TimeoutError, urllib3.exceptions.SSLError, urllib3.exceptions.MaxRetryError, urllib3.exceptions.ProtocolError) as e:
+                if attempt < 2:
+                    time.sleep(1 + attempt)
+                    continue
+                print(f"  x calendar: {type(e).__name__} after {attempt+1} retries")
+                return None
             except Exception as e:
                 if attempt < 2:
+                    time.sleep(1 + attempt)
                     continue
                 print(f"  x calendar: {e}")
                 return None