refactor: 共享请求管道、按需懒加载、流式内存护栏与连接池治理

- 抽取 ApiRequestPipeline 单例，44 个路由文件共享同一实例
- Handler/Adapter 模块级 __getattr__ 延迟导入，减少启动时间
- 新增 ensure_stream_buffer_limit() 流式内存护栏（16MB 单行 / 32MB 总量）
- HTTP 空闲连接清理与 curl_cffi LRU 会话池
- ensure_providers_bootstrapped 按需引导指定 provider_types
- Usage 事件序列化迁移至 msgpack，Redis codec 隔离
- 启动预热任务（/readyz 就绪门控）与优雅关闭
- 通知邮件模块独立开关与 SMTP 配置校验
- CryptoService DCL 线程安全修复
- 通知模块开关 DB 查询 30s 内存缓存
- /readyz 对 unknown 状态返回 503
- 预热关闭 5s 超时保护
- 预热适配器逐个 try-except 容错
- FormatConversionRegistry 哨兵模式防并发重复物化
- 流式缓冲检查无条件执行

Closes #230

Co-authored-by: AAEE86 <[email protected]>

tests/unit/test_curl_cffi_transport_pool.py

@@ -0,0 +1,40 @@
+from __future__ import annotations
+
+from collections import OrderedDict
+
+import pytest
+
+import src.clients.curl_cffi_transport as transport_module
+
+
+class _DummySession:
+    def __init__(self, **kwargs: object) -> None:
+        self.kwargs = kwargs
+        self.close_calls = 0
+
+    async def close(self) -> None:
+        self.close_calls += 1
+
+
+@pytest.mark.asyncio
+async def test_get_or_create_session_uses_lru_eviction(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setattr(transport_module, "AsyncSession", _DummySession, raising=False)
+    monkeypatch.setattr(transport_module, "_MAX_SESSIONS", 2, raising=False)
+    monkeypatch.setattr(transport_module, "_session_pool", OrderedDict(), raising=False)
+
+    s1 = await transport_module._get_or_create_session("chrome120", "http://p1")
+    s2 = await transport_module._get_or_create_session("chrome120", "http://p2")
+
+    # 命中 s1 使其变成最近使用，随后新增 s3 应淘汰 s2。
+    s1_hit = await transport_module._get_or_create_session("chrome120", "http://p1")
+    assert s1_hit is s1
+
+    s3 = await transport_module._get_or_create_session("chrome120", "http://p3")
+    assert isinstance(s3, _DummySession)
+
+    assert len(transport_module._session_pool) == 2
+    assert "chrome120::http://p1" in transport_module._session_pool
+    assert "chrome120::http://p3" in transport_module._session_pool
+    assert "chrome120::http://p2" not in transport_module._session_pool
+    assert s2.close_calls == 1
+    assert s1.close_calls == 0