Added packet manipulation dupe glitches fixes

[GrapJeje]

Async Vault Saving with Anti-Dupe Protection

Problem:

• Vault saves block main thread (server lag)
• Race conditions cause data corruption
• Players can exploit packet manipulation to dupe items
• No verification after writes

Solution
Implement async saves with per-player locking and anti-dupe validation.

Changes

• Async Saves - File I/O in background thread pool (zero lag)
• Per-Player Locks - Only one save per player at a time
• Atomic Writes - Temp file + rename (no corruption on crash)
• Verification - Reload and validate after save
• Anti-Dupe Checks - Block saves < 500ms, validate item amounts

Result

• ✅ Zero server lag during saves
• ✅ No data corruption from concurrent writes
• ✅ Packet duping exploits blocked
• ✅ Fully backwards compatible