Support sqlalchemy.Table and sqlalchemy.Metadata in Python SDK

Add support for `sqlalchemy.Table` and `sqlalchemy.Metadata` .

Look at the Python SDK code for OpenMLDB to understand how it currently interacts with SQLAlchemy. Identify where sqlalchemy.Table and sqlalchemy.Metadata objects are handled or missing. Check existing tests for SQLAlchemy integration to see the pattern. Determine what changes are needed to support these types, likely in the serialization or query generation layer.

由索引模型根据 Issue 内容生成。