[feature] Add Lua mod infrastructure (OnMonsterDeath, OnItemUse hooks)

[yuripourre]

Provides the C++ bindings and Lua events needed to implement the soulstone mod

New events (assets/lua/devilutionx/events.lua):

• OnMonsterDeath(monster, deathFrame) - fires every death-animation frame
• OnItemUse(player, item) -> bool - cancellable item-use event
• CreateCancellableEvent() helper

New devilutionx.game module:

• game.prepDoEnding() - trigger the win-screen sequence
• game.isQuestDone(questId) - check quest completion state
• game.isMultiplayer() - multiplayer detection

Extended devilutionx.monsters:

• monster.typeId - integer type ID
• monster.name - display name

Extended devilutionx.player:

• player:isOnLevel(n) - dungeon-level check
• player:say(speech) - hero speech
• player.isMyPlayer - local-player flag
• player.level - current dungeon level
• player.HeroSpeech - enum

Extended devilutionx.items:

• items.spawnQuestItem(itemIdx, x, y, sendmsg) - spawn with network sync

C++ hooks (no-ops when no Lua mod is registered):

• LuaEvent("OnMonsterDeath", ...) in MonsterDeath(), before the vanilla Diablo death sequence.
• LuaEventCancellable("OnItemUse", ...) in UseInventoryItem(), after all existing guards and before the default item-processing path.

[Trihedraf]

This looks good and a big chunk of really useful hooks 👍

[yuripourre]

This looks good and a big chunk of really useful hooks 👍

Yeah, I am eager to revive the soulstone mod! Dreaming with an "Act 2" mod. 🤩

[yuripourre]

@Trihedraf thanks for reviewing!

[yuripourre]

This PR can be simiplified, I will refactor this and re-activate when done.