Fix critical blockchain desynchronization issue with out-of-order block handling

CRITICAL FIXES:
- Add block buffering for out-of-order blocks (pending_blocks HashMap)
- Implement immediate P2P request for missing blocks via sync_blocks()
- Add DDoS protection with rate limiting (max 10 concurrent requests, 10s cooldown)
- Implement parallel processing of consecutive blocks (up to 10 blocks like Solana)
- Add automatic retry mechanism with exponential backoff (max 3 retries)
- Add periodic cleanup of stale buffers (60s timeout)

GENESIS FIXES:
- Implement deterministic Genesis block signature using SHA3-256
- Add Genesis creation coordination (only node_001 creates in bootstrap mode)
- Ensure Genesis block is saved with retry mechanism (panic on failure)
- Add validation for Genesis block before creating block #1
- Improve previous_hash validation for all blocks including Genesis

ARCHITECTURE:
- Pass unified_p2p to process_received_blocks for P2P operations
- Use dual-channel approach (block_rx + retry_rx) with priority for retries
- Maintain compatibility with existing Turbine and Reed-Solomon protocols
- Scale for millions of nodes with proper resource management

This resolves the split-brain issue where nodes would get stuck when blocks arrived out of order, particularly when block N+1 arrived before block N due to network delays.

Author: AIQnetLab