fix: Prevent world ticking thread hang during ItemEntity#mergeWithNeighbours (#802)

[Kameshekf]

Resolves #802

Summary of the Problem

When parallel-world-ticking: enabled: true is active on servers with high-density item drops (such as carpet duper machines, sand duplicators, or high-yield mob farms), ItemEntity#mergeWithNeighbours() causes the Leaf Level Ticking Thread - world to freeze/deadlock in ca.spottedleaf.moonrise.patches.chunk_system.level.entity.ChunkEntitySlices$EntityCollectionBySection.getEntities.

The hang occurred due to two main factors:

1. Tick Synchronization Spike: Thousands of simultaneously spawned items attempted mergeWithNeighbours() on the exact same tick cycle (this.tickCount % i == 0).
2. Unbounded Iteration: When massive item piles gather, getEntitiesOfClass() yields an enormous collection of nearby items, leading to excessive lock contention and CPU starvation across parallel world threads.

Solution

1. Phase-offset merge ticks: Spread item merge checks across ticks using (this.tickCount + this.getId()) % i == 0, eliminating synchronized tick spikes.
2. Bounded merge iteration: Limit maximum merge attempts to 32 items per entity per merge pass (mergedCount >= 32).

Testing & Verification

• Tested with 5,000+ duplicated items in a single chunk with parallel-world-ticking: true.
• Zero thread hangs, zero deadlocks, and watchdog TPS remains completely stable.