Improve concurrency handling and async processing in DefenderWorker

[Killer-oooo]

This PR refactors DefenderWorker to improve concurrency safety and async handling.

Changes:

• Introduced ConcurrentDictionary to prevent duplicate attack processing
• Added TTL-based tracking for handled attacks
• Replaced Task.Factory.StartNew with Task.Run
• Updated attack handling to use proper async/await flow
• Cleaned up obsolete comments and streamlined logic

Impact:

• Prevents duplicate or parallel processing of the same attack
• Improves thread safety
• Ensures controlled and sequential attack handling
• Modernizes async usage to current best practices

No other components were modified.