Fix XP orb spawning to use queue system to prevent client lag on large amounts of xp spawns

[SkyzerFlyzer]

This commit fixes all XP orb spawning issues by implementing a proper queue system and respecting Minecraft's 16-bit integer limit.

Problems Fixed

1. All XP orbs spawned instantly

   • Previously: Loop spawned all orbs immediately in one tick
   • Now: XP orbs queue and spawn gradually over time

2. Doesn't respect 32,767 max orb value

   • Previously: Always used orbSize, never considered limit
   • Now: Clamps to MAX_ORB_VALUE = 32767 (16-bit signed int)

3. Last orb value bug

   • Previously: 2502 XP with size 5 → 501×5 = 2505 XP (3 extra!)
   • Now: 2502 XP with size 5 → 500×5 + 1×2 = 2502 XP ✓

4. XP orbs spawn at least 3x faster than items

   • Previously: Items spawned at 3-10 per cycle
   • Now: XP spawns at 30 per cycle (minimum 3x faster)
   • Prevents long delays with large XP rewards

Implementation

GatewayEntity.java:

• Added Queue<Integer> undroppedXP field
• Added spawnXPOrb(int value) method
• Added queueXP(int value) method
• Added getXPDropCount() returning 30 (3x faster than items)
• Updated tick() to spawn XP orbs in parallel with items
• Added NBT serialization for XP queue (save/load)
• Added ExperienceOrb import

NormalGatewayEntity.java:

• Updated isCompleted() to check XP queue is empty

Reward.java (ExperienceReward):

• Added MAX_ORB_VALUE = 32767 constant
• Changed to queue XP instead of spawning directly
• Fixed remainder calculation: Math.min(remaining, clampedOrbSize)
• Respects 32,767 limit by clamping orbSize

Technical Details

XP orbs now follow same pattern as items:

• Queue during reward generation
• Spawn gradually every 4 ticks via tick()
• Persist across world reloads (NBT)
• Gateway waits for all XP to spawn before completing

Spawn rate: 30 XP orbs per 4 ticks (vs 3-10 items per 4 ticks)

Fixes: All reported XP orb spawning issues