Refactor users creating separate classes, service and repository

src/models/__init__.py

@@ -1,12 +1,15 @@
 from .credential import Credential
 from .gate import Gate
 from .status import Status
-from .users import Users, Role
+from .user import User
+from .grant import Grant
+from .role import Role
 
 __all__ = [
     "Credential",
     "Gate",
     "Status",
-    "Users",
-    "Role"
+    "User",
+    "Role",
+    "Grant"
 ]