整理配置和代码入口，增加部分测试。

sync_state_machine/datasource/__init__.py

@@ -17,6 +17,9 @@ from .task_result import TaskResult, TaskStatus
 # API DataSource
 from .api import ApiClient, ApiDataSource, BaseApiHandler
 
+# DB DataSource
+from .db import DbDataSource, BaseDbHandler
+
 # JSONL DataSource  
 from .jsonl import JsonlDataSource, BaseJsonlHandler
 
@@ -34,6 +37,10 @@ __all__ = [
     "ApiClient",
     "ApiDataSource",
     "BaseApiHandler",
+
+    # DB DataSource
+    "DbDataSource",
+    "BaseDbHandler",
     
     # JSONL DataSource
     "JsonlDataSource",