Translate the stat name in RBY's X-item and vitamin rose! messages

Both the player-side and AI-trainer stat-rise messages (X ATTACK/
DEFENSE/etc. and the vitamins) passed the raised stat's name as a raw
uppercase Lua string (stat:upper()), bypassing Strings() entirely, so
it always rendered in English regardless of the active language even
though the surrounding sentence template was already translated.

Wrap the substituted stat name in Strings() at every call site
(src/inventory/ItemEffects.lua's two player-side messages and
src/battle/TrainerAI.lua's AI-trainer X-item message, found in
review), reusing the same "ATTACK"/"DEFENSE"/"SPEED"/"SPECIAL"/"HP"
keys SummaryMenu.lua's stat labels already look up the same way.

src/battle/TrainerAI.lua

@@ -124,7 +124,7 @@ function TrainerAI.useItem(battle, item)
   elseif X_STAT[item] then
     local stat = X_STAT[item]
     enemy.stages[stat] = math.min(6, (enemy.stages[stat] or 0) + 1)
-    table.insert(msgs, Strings("%s's\n%s rose!", displayName(enemy), stat:upper()))
+    table.insert(msgs, Strings("%s's\n%s rose!", displayName(enemy), Strings(stat:upper())))
   elseif item == "GUARD_SPEC" then
     enemy.mist = true
     table.insert(msgs, Strings("%s's\nprotected against\nstat changes!", displayName(enemy)))

src/inventory/ItemEffects.lua

@@ -294,7 +294,7 @@ function ItemEffects.use(data, save, itemId, target, battle, moveIndex, ow)
           "Nothing happened!") }
       end
       b.stages[stat] = cur + 1
-      return "consumed", { Strings("%s's\n%s rose!", b.name, stat:upper()) }
+      return "consumed", { Strings("%s's\n%s rose!", b.name, Strings(stat:upper())) }
     end
     -- ItemUseDireHit/ItemUseGuardSpec always set the bit and consume
     -- the item, even when it is already active
@@ -493,7 +493,7 @@ function ItemEffects.use(data, save, itemId, target, battle, moveIndex, ow)
     -- Spanish ROM puts the stat before the name), so the extracted line
     -- cannot be filled positionally; the engine wording stands
     return "consumed", { Strings("%s's %s\nrose!", monName(data, target),
-      vitaminStat == "hp" and "HP" or vitaminStat:upper()) }
+      Strings(vitaminStat == "hp" and "HP" or vitaminStat:upper())) }
   end
 
   -- PP UP boosts the move the player picked (ItemUsePPUp's move menu)