feat: 数据采集健壮性改进

- 新增 src/core/retry.py: 指数退避 + 抖动的重试装饰器
- bzzoiro: 改进重试逻辑
  - 429/5xx/网络错误均触发指数退避重试
  - 4xx 直接抛(不重试)
- understat: 新增重试(原无重试)
- injuries: 新增重试 + 文件缓存 7 天过期
- sources.py: 延迟导入修复循环导入

src/data/understat.py

@@ -4,8 +4,10 @@
 """
 from __future__ import annotations
 
+import asyncio
 import json
 import logging
+import random
 import re
 
 from src.core.http_client import get_client
@@ -41,9 +43,24 @@ async def fetch_understat(league_code: str, season: int) -> list[dict]:
         "Referer": f"https://understat.com/league/{understat_league}/{season}",
     }
 
-    client = get_client()
-    resp = await client.get(url, headers=headers)
-    resp.raise_for_status()
+    # 重试:网络错误 / 5xx / 429
+    last_exc: Exception | None = None
+    for attempt in range(3):
+        try:
+            client = get_client()
+            resp = await client.get(url, headers=headers, timeout=30)
+            resp.raise_for_status()
+            break
+        except Exception as e:
+            last_exc = e
+            if attempt == 2:
+                raise
+            delay = min(2 ** attempt, 8) + random.uniform(0, 1)
+            logger.warning("understat fetch failed, retry %d in %.1fs: %s", attempt + 1, delay, e)
+            await asyncio.sleep(delay)
+    else:
+        raise RuntimeError(f"understat fetch failed: {last_exc}")
+
     # understat 返回 JS 对象,需要提取 JSON
     text = resp.text
     # 匹配 var datesData = JSON.parse('...');