New engine features: Add runtime item resources creation and tweak op122/255

[4Luke4]

This pull request introduces a robust system for creating, copying, persisting, and restoring in-memory ITM (item) resources, along with related opcode and marshalling infrastructure. The core changes enable items to be dynamically created, modified, and saved across game sessions, with hooks for engine integration and opcode extension.

The most important changes are:

Item Creation, Copying, and Persistence (EEex_Item):

• Added EEex_Item.lua, which implements functions to create new in-memory items (EEex_Item_CreateFromResref), copy existing items (EEex_Item_CreateCopy), and manage persistent item resources, including marshaling and unmarshaling item state for save/load support. This includes validation, resource management, and header override logic.
• Added infrastructure for tracking which items should persist across saves, and for serializing/deserializing their data as hex blobs.

Marshalling Integration:

• Integrated item persistence with the game's marshalling system: only the first portrait sprite carries the item marshal payload, and unmarshaling is gated to occur once per game-state lifetime. Listeners reset the unmarshaled state when the game state is destroyed.
• Registered EEex_Item with the startup file list to ensure the new item logic is loaded at game initialization.

Opcode and Engine Hook Extensions:

• Added hooks for CGameEffectCreateItem (opcodes #122/#255), allowing pre- and post-processing when items are created by effects. This enables custom item flags/logic to be injected before and after the engine places the item. [1] [2]

These changes provide a foundation for dynamic, persistent, and extensible item handling in the engine, with deep integration into the save/load and effect processing systems.

Requires: Bubb13/InfinityLoader#5.
Requires: #116.