Makes obj_integrity only updated through procs (#59474)

Having things updating integrity directly is just going to cause more problems down the line as more elements and components depend on being notified of integrity changes. It's an easy mistake to make so making it private should deal with the problem.

get_integrity() might be useful in the future but is mainly a side effect of making obj_integrity private as that also disallows reads.

code/game/objects/structures/plaques/_plaques.dm

@@ -53,7 +53,7 @@
 		unwrenched_plaque.desc = desc
 		unwrenched_plaque.engraved = engraved
 	unwrenched_plaque.icon_state = icon_state
-	unwrenched_plaque.obj_integrity = obj_integrity
+	unwrenched_plaque.update_integrity(get_integrity())
 	unwrenched_plaque.setDir(dir)
 	qdel(src) //The plaque structure on the wall goes poof and only the plaque item from unwrenching remains.
 	return TRUE
@@ -183,6 +183,6 @@
 		placed_plaque.desc = desc
 		placed_plaque.engraved = engraved
 	placed_plaque.icon_state = icon_state
-	placed_plaque.obj_integrity = obj_integrity
+	placed_plaque.update_integrity(get_integrity())
 	placed_plaque.setDir(dir)
 	qdel(src)