Replaces static Item.ItemList and related collections with thread-safe data structures using ConcurrentDictionary and ImmutableHashSet. Adds thread-safe helpers for marking items for deconstruction and managing item lists. Updates all usages of Item.ItemList and DeconstructItems to use new APIs, improving performance and safety in multi-threaded contexts. Also refactors MeleeWeapon and Projectile impact queues to use ConcurrentQueue, and updates related logic throughout the codebase.
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