During initialisation of Tools, each new mod no longer makes a copy
of every data object from the parent mod. Instead, a new object is
created when and only when the mod actually makes changes to a
particular object. In other words, this is a "copy-on-write" system.
Damage categories are now read using .getCategory, which gen 3 overrides.
move.category can still be read directly to check if something's a status
move, but it should never be used for reading damage categories.
This also fixes a crash in gen 3 and makes it playable again.
