feat(mixin): add TableBaseMixin and UUIDTableBaseMixin for async CRUD operations

- Implemented TableBaseMixin providing generic CRUD methods and automatic timestamp management.
- Introduced UUIDTableBaseMixin for models using UUID as primary keys.
- Added ListResponse for standardized paginated responses.
- Created TimeFilterRequest and PaginationRequest for filtering and pagination parameters.
- Enhanced get_with_count method to return both item list and total count.
- Included validation for time filter parameters in TimeFilterRequest.
- Improved documentation and usage examples throughout the code.

models/base/__init__.py

@@ -1,2 +1,12 @@
+"""
+SQLModel 基础模块
+
+包含：
+- SQLModelBase: 所有 SQLModel 类的基类（真正的基类）
+
+注意：
+    TableBase, UUIDTableBase, PolymorphicBaseMixin 已迁移到 models.mixin
+    为了避免循环导入，此处不再重新导出它们
+    请直接从 models.mixin 导入这些类
+"""
 from .sqlmodel_base import SQLModelBase
-from .table_base import TableBase, UUIDTableBase, now, now_date