perf: 优化流式响应内存占用和正则预编译

- 添加 record_parsed_chunks 标志，仅在 FULL 日志级别时累积 parsed_chunks
- 预编译 CJK 和敏感信息正则表达式，避免重复编译
- 优化 header 脱敏循环，预计算 lowercase 集合
- 移除 consumer_streams.py 中未使用的 message_fields 变量
- 将 SystemConfigService import 移至文件顶部

src/services/task/service.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import re
 from collections.abc import Callable
 from typing import Any
 
@@ -18,6 +19,11 @@ from src.services.task.exceptions import TaskNotFoundError
 from src.services.task.protocol import AttemptKind, AttemptResult
 from src.services.task.schema import ExecutionResult, TaskStatusResult
 
+_SENSITIVE_PATTERN = re.compile(
+    r"(api[_-]?key|token|bearer|authorization)[=:\s]+\S+",
+    re.IGNORECASE,
+)
+
 
 class TaskService:
     """
@@ -883,7 +889,6 @@ class TaskService:
         - stop on "client error" (raise UpstreamClientRequestError)
         - if all failed, raise AllCandidatesFailedError
         """
-        import re
         from datetime import datetime, timezone
 
         import httpx
@@ -901,11 +906,6 @@ class TaskService:
         from src.services.orchestration.error_classifier import ErrorClassifier
         from src.services.system.config import SystemConfigService
 
-        _SENSITIVE_PATTERN = re.compile(
-            r"(api[_-]?key|token|bearer|authorization)[=:\s]+\S+",
-            re.IGNORECASE,
-        )
-
         def _sanitize(message: str, max_length: int = 200) -> str:
             if not message:
                 return "request_failed"