app.storage.tab is only persistent when using Redis

This allows storing non-serializable data in "normal" circumstances.

nicegui/storage.py

@@ -66,7 +66,7 @@ class Storage:
     def __init__(self) -> None:
         self._general = Storage._create_persistent_dict('general')
         self._users: Dict[str, PersistentDict] = {}
-        self._tabs: Dict[str, PersistentDict] = {}
+        self._tabs: Dict[str, ObservableDict] = {}
 
     @staticmethod
     def _create_persistent_dict(id: str) -> PersistentDict:  # pylint: disable=redefined-builtin
@@ -163,13 +163,19 @@ def tab(self) -> observables.ObservableDict:
     async def _create_tab_storage(self, tab_id: str) -> None:
         """Create tab storage for the given tab ID."""
         if tab_id not in self._tabs:
-            self._tabs[tab_id] = Storage._create_persistent_dict(f'tab-{tab_id}')
-            await self._tabs[tab_id].initialize()
+            if Storage.redis_url:
+                self._tabs[tab_id] = Storage._create_persistent_dict(f'tab-{tab_id}')
+                await self._tabs[tab_id].initialize()
+            else:
+                self._tabs[tab_id] = ObservableDict()
 
     def copy_tab(self, old_tab_id: str, tab_id: str) -> None:
         """Copy the tab storage to a new tab. (For internal use only.)"""
         if old_tab_id in self._tabs:
-            self._tabs[tab_id] = Storage._create_persistent_dict(f'tab-{tab_id}')
+            if Storage.redis_url:
+                self._tabs[tab_id] = Storage._create_persistent_dict(f'tab-{tab_id}')
+            else:
+                self._tabs[tab_id] = ObservableDict()
             self._tabs[tab_id].update(self._tabs[old_tab_id])
 
     async def prune_tab_storage(self) -> None: