Pass data through to ItemEffects.partyAction for Gen 2 pack items

Both call sites -- Game2:usePartyItem (the field pack) and
BattleState:useItem (the battle pack) -- asked ItemEffects.partyAction
for an item's family with no `data` argument, even though every other
call in the same functions (useOnMon, usePpItem, applyPartyItem) passed
it through correctly. partyAction resolves through recordFor, which
reads data.gen2ItemEffects when given a dataset and falls back to the
module's own built-in RECORDS table when not -- so with no data, a
mod's own item_effects record was invisible and every mod-defined Gen 2
field or battle item resolved to a nil action, falling straight through
to "isn't going to help here" / "isn't going to help here" without ever
opening the party picker.

Both now pass the live dataset (self.data on Game2, self.game.data on
the battle screen) the same way their sibling calls already did.

tests/gen2_battle_items_test.lua

@@ -117,6 +117,27 @@ local DATA = {
       fieldMenu = "ITEMMENU_PARTY", battleMenu = "ITEMMENU_NOUSE" },
     OLD_ROD = { id = "OLD_ROD", pocket = "KEY", name = "OLD ROD",
       fieldMenu = "ITEMMENU_CURRENT", battleMenu = "ITEMMENU_NOUSE" },
+    -- a mod's own battle-pack item: its action lives only in
+    -- gen2ItemEffects below, which ItemEffects.RECORDS (the module's
+    -- built-in table) has never heard of (#8)
+    MOD_ITEM = item("MOD_ITEM"),
+  },
+  gen2ItemEffects = {
+    -- a status cure rather than an HP heal: HP is exposed to the wild
+    -- mon's own reply once the item spends the turn, which would make a
+    -- direct before/after HP check depend on incidental battle math this
+    -- fix has nothing to do with.  Status is not.
+    MOD_ITEM = {
+      action = "status", field = true, needsTarget = true,
+      use = function(ctx)
+        local mon = ctx.mon
+        if mon.status ~= "poison" then
+          return { used = false, text = "It won't have\nany effect." }
+        end
+        mon.status = nil
+        return { used = true, text = "MOD ITEM used!" }
+      end,
+    },
   },
 }
 
@@ -236,6 +257,33 @@ do
   eq(save.inventory.ANTIDOTE, 1, "with the ANTIDOTE untouched")
 end
 
+-- ---- a mod's own battle-pack item (#8) -------------------------------------
+-- BattleState:useItem asked ItemEffects.partyAction for the item's family
+-- with no `data` argument, the same omission Game2:usePartyItem had for the
+-- field pack, so a mod item's action -- present only in the merged
+-- gen2ItemEffects table -- resolved to nil and the pack fell straight to
+-- "That isn't going to help here." instead of opening the party list.
+do
+  local sick = Mon.new(DATA, "CYNDAQUIL", 10, { dvs = perfect })
+  sick.moves = { { id = "TACKLE", pp = 35, maxPp = 35 } }
+  sick.status = "poison"
+  local screen, _, _, save, pushed = newScreen({
+    player = sick, party = { sick }, inventory = { MOD_ITEM = 1 },
+  })
+  check(runToMenu(screen), "reached the menu")
+
+  screen:useItem("MOD_ITEM")
+  eq(screen.phase, "submenu",
+    "a mod's own gen2ItemEffects record opens UseItem_SelectMon")
+  local picker = pushed[#pushed]
+  eq(getmetatable(picker), PartyMenu, "and the pick is the party screen")
+  if picker and picker.onChoose then
+    picker.onChoose(1, sick)
+    eq(sick.status, nil, "the mod item's own use() ran through the real screens")
+    eq(save.inventory.MOD_ITEM, nil, "and the mod item was spent")
+  end
+end
+
 -- ---- IsItemUsedOnConfusedMon: the battle-only arm --------------------------
 do
   local screen, battle, player, save, pushed = newScreen({