Refactor REST API item classes and access methods

- Changed various item classes from ItemDictType to BaseRestItem for consistency.
- Updated ManagedObjectDictType to ManagedObjectItem.
- Replaced ensure_has_access method calls with check_access for improved clarity.
- Refactored GUI composition methods to utilize the new GuiBuilder utility.
- Adjusted return types in get_items methods to use ItemsResult for better type safety.
- Removed deprecated field handling in BaseModelHandler.
- Enhanced type annotations across multiple modules for better type checking.

server/src/uds/REST/methods/services_pool_groups.py

@@ -50,7 +50,7 @@ if typing.TYPE_CHECKING:
 # Enclosed methods under /item path
 
 
-class ServicePoolGroupItem(types.rest.ItemDictType):
+class ServicePoolGroupItem(types.rest.BaseRestItem):
     id: str
     name: str
     comments: str