Dispose controls only on session closed event

Fix #1267
Fix #1272
Fix #1274
Fix #1279
Fix #1280

Author: FeodorFitsner

sdk/python/packages/flet-core/src/flet_core/page.py

@@ -334,7 +334,6 @@ def _clean(self, control: Control):
             self._send_command("clean", [control.uid])
             for c in removed_controls:
                 c.will_unmount()
-                c._dispose()
 
     async def _clean_async(self, control: Control):
         async with self.__async_lock:
@@ -348,7 +347,6 @@ async def _clean_async(self, control: Control):
             await self._send_command_async("clean", [control.uid])
             for c in removed_controls:
                 await c.will_unmount_async()
-                c._dispose()
 
     def _close(self):
         removed_controls = self._remove_control_recursively(self.index, self)
@@ -428,14 +426,12 @@ def __update_control_ids(self, added_controls, results):
     def __handle_mount_unmount(self, added_controls, removed_controls):
         for ctrl in removed_controls:
             ctrl.will_unmount()
-            ctrl._dispose()
         for ctrl in added_controls:
             ctrl.did_mount()
 
     async def __handle_mount_unmount_async(self, added_controls, removed_controls):
         for ctrl in removed_controls:
             await ctrl.will_unmount_async()
-            ctrl._dispose()
         for ctrl in added_controls:
             await ctrl.did_mount_async()