Fixes preferences resetting (#3104)

## About The Pull Request
Fixes https://github.com/Bubberstation/Bubberstation/issues/2879

The reason for the issue seems rooted in skyrat's own port of the
original json configs on tg (or perhaps the loads of changes they've
made to it over the years). This pr patches it so that characters won't
reset between rounds.

original fixes by smartkar
## Why It's Good For The Game
Guess
## Proof Of Testing
<details>
<summary>Screenshots/Videos</summary>


![qe0kfreu8l](https://github.com/user-attachments/assets/c84b20a1-c09b-4905-b682-3c280c7e8ab3)


</details>
It saves the character on creation and works fine after re-accessing the
savefile

## Changelog
🆑
fixes: fixes the issue where characters would reset after a round or on
switching character slots
/🆑

modular_zubbers/code/modules/client/verbs/character_directory.dm

@@ -84,6 +84,7 @@ GLOBAL_DATUM(character_directory, /datum/character_directory)
 /// Saves us on copypaste code
 /datum/preference/choiced/directory_character_prefs
 	savefile_key = "char_directory_char_prefs" // This is so unit checks don't scream
+	abstract_type = /datum/preference/choiced/directory_character_prefs
 
 /datum/preference/choiced/directory_character_prefs/init_possible_values()
 	return list("Yes", "No", "No ERP", "Check OOC", "Unset", "Maybe")