Fix GUI concurrent access and autocrafter deadlock

[Distolfix]

Summary

This PR fixes three critical issues: GUI concurrent access crashes, autocrafter deadlock, and WildStacker/UltimateStacker item loss.

Problems Fixed

1. GUI Concurrent Access (ConcurrentModificationException)

Multiple players opening the same hopper GUI simultaneously caused server crashes due to unsynchronized iterator access in the GUI update task.

2. Autocrafter Deadlock

When autocrafter was active, it would fill all 5 slots (ingredients + output), preventing any new items from being added. The hopper would become permanently stuck with items unable to enter.

3. WildStacker/UltimateStacker Item Loss

Two separate bugs causing hundreds of items to disappear:

• Event emission bug: Suction emitted InventoryPickupItemEvent even when hopper was full, causing stacker plugins to modify entity amounts incorrectly
• Slot reservation bug: Overly conservative slot counting prevented pickup even with 2-3 free slots available

Solutions

GUI Thread Safety

• Added synchronizedList() wrapper for GUI update task viewer list
• Ensures thread-safe iteration when multiple players access same hopper
• Prevents ConcurrentModificationException crashes

Autocrafter Slot Reservation

• Modified suction and hopper transfer modules to reserve 1 empty slot when autocrafter is active
• Hopper maintains at least 1 free slot for craft output
• Uses reserveOneSlot parameter in addAny() to enforce reservation

WildStacker Item Loss Fixes

• Suction fix: Move addAny() before event emission, only emit event when added > 0
• Cache fix: Calculate usable slots correctly: (freeSlots - 1) when reserving
• Partial stacks: Allow filling partial stacks regardless of slot reservation (doesn't consume slots)

Technical Details

Thread Safety Implementation

private final List<UUID> viewers = Collections.synchronizedList(new ArrayList<>());

Slot Reservation Logic

// In suction: reserve slot if autocrafter present
boolean hasAutoCrafter = hopper.getLevel().getModule("AutoCrafting") != null;
int added = hopperCache.addAny(itemStack, toAdd, hasAutoCrafter);

// In cache: track usable slots
int usableFreeSlots = reserveOneSlot ? (freeSlots - 1) : freeSlots;

Event Emission Fix

// Try adding first
int added = hopperCache.addAny(itemStack, toAdd, hasAutoCrafter);

// Only emit event if we actually added items
if (added == 0) {
    continue; // Skip without emitting event
}

// Now safe to emit event
InventoryPickupItemEvent pickupEvent = new InventoryPickupItemEvent(hopperInventory, item);

Testing

• ✅ Multiple players opening same hopper GUI simultaneously - no crashes
• ✅ Autocrafter with full inventory - new items can still enter
• ✅ 10,000 diamonds with suction + autocrafter + WildStacker - no item loss
• ✅ Items with 2-3 free slots are now properly collected
• ✅ Partial stacks filled even when reserving slot for autocrafter

Compatibility

• Compatible with WildStacker, UltimateStacker, and RoseStacker
• Backwards compatible with vanilla and non-stacker setups
• No breaking changes to existing functionality