feat: replace declarative_base -> DeclarativeBase for sqlalchemy 2.0 …

…migration (#65)

* Replace declarative_base -> DeclarativeBase for sqlalchemy 2.0 migration

* Update adapter.py

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Co-authored-by: Eric Luo <hsluoyz@qq.com>

casbin_sqlalchemy_adapter/adapter.py

@@ -3,10 +3,11 @@
 from casbin import persist
 from sqlalchemy import Column, Integer, String
 from sqlalchemy import create_engine, or_
-from sqlalchemy.ext.declarative import declarative_base
-from sqlalchemy.orm import sessionmaker
+from sqlalchemy.orm import sessionmaker, DeclarativeBase
 
-Base = declarative_base()
+# declarative base class
+class Base(DeclarativeBase):
+    pass
 
 
 class CasbinRule(Base):