perf: major optimization of tab/command system and config access

Replaced O(n²) logic with HashSet-based lookups, removed repeated config access, and optimized command/tab processing paths.

Key improvements:

• Replaced List.contains with HashSet in tab filtering
• Optimized getExtendsTabCommands from O(n²) to Set-based approach
• Cached is_network config to avoid repeated getBoolean calls
• Replaced reflection-based Sound lookup with direct valueOf
• Replaced addUnique with LinkedHashSet-based merging
• Made plugin message handling more efficient
• Reduced repeated string parsing and allocations in hot paths
• Improved async update checker to CompletableFuture-based execution
• Replaced HashMap with ConcurrentHashMap where needed

Overall: reduced CPU overhead in hot events (TAB, commands, messaging) and improved thread safety.