♻️ Update model_fields, type them with compatibility for Pydantic v3

Author: tiangolo

sqlmodel/main.py

@@ -477,7 +477,7 @@ def Relationship(
 class SQLModelMetaclass(ModelMetaclass, DeclarativeMeta):
     __sqlmodel_relationships__: Dict[str, RelationshipInfo]
     model_config: SQLModelConfig
-    model_fields: Dict[str, FieldInfo]
+    model_fields: ClassVar[Dict[str, FieldInfo]]
     __config__: Type[SQLModelConfig]
     __fields__: Dict[str, ModelField]  # type: ignore[assignment]