include/structs: Change on hit spells to CExoArrayList_ptr
include/structs: CNWSpell was the incorrect size.
include/structs: update CNWSpellArray.h

- First field is a uint32_t indicating size.
plugins/combat: Redo item on hit cast spells.

Note that this provides different behavior to the NWN
engine which only applies one OnHitCastSpell property per
item.  Instead this applies all of them.  As such...
it's possible that items loaded down with them could
cause performance degradation that would not be caused
in vanilla NWN.