Core: Add restricted_dumps helper (#5117)

* Add pickling helper that check unpicklability

* Add test condition and generation error handling

* Fix incorrect call and make imports consistent

* Fix newline padding

* Change PicklingError to directly caused by UnpicklingError

Co-authored-by: Doug Hoskisson <beauxq@users.noreply.github.com>

* Revert to `pickle.dumps` for decompressed multidata

* Fix import order

* Restore pickle import in main

* Re-add for multidata in Main

* Remove multisave checks

* Update MultiServer.py

* Update customserver.py

---------

Co-authored-by: Doug Hoskisson <beauxq@users.noreply.github.com>
Co-authored-by: NewSoupVi <57900059+NewSoupVi@users.noreply.github.com>

MultiServer.py

@@ -546,6 +546,7 @@ class Context:
 
     def _save(self, exit_save: bool = False) -> bool:
         try:
+            # Does not use Utils.restricted_dumps because we'd rather make a save than not make one
             encoded_save = pickle.dumps(self.get_save())
             with open(self.save_filename, "wb") as f:
                 f.write(zlib.compress(encoded_save))