Implement Raft consensus algorithm for distributed systems simulator

This commit adds a complete implementation of the Raft consensus algorithm,
providing a robust solution for achieving consensus in distributed systems.

Key features implemented:
- Three-state system: Follower, Candidate, and Leader states
- Leader election with randomized election timeouts (150-300ms)
- Log replication for state machine commands
- Heartbeat mechanism to maintain leader authority
- Safety guarantees through term numbers and log consistency checks
- Proper handling of split votes and network partitions

Implementation details:
- Added VSRaftProtocol.java with full Raft algorithm logic
- Integrated with existing event-driven simulation framework
- Supports dynamic cluster sizes with proper quorum calculations
- Implements RequestVote and AppendEntries RPCs
- Maintains persistent state (currentTerm, votedFor, log entries)
- Includes comprehensive logging for debugging and visualization

Testing:
- Added VSRaftProtocolTest.java with unit tests covering:
  - Leader election scenarios
  - Log replication mechanics
  - State transitions
  - Message handling for all RPC types

Integration:
- Registered protocol in VSRegisteredEvents for simulator discovery
- Added human-readable names in VSDefaultPrefs for UI display
- Compatible with existing visualization and timing systems

This implementation follows the Raft paper closely while adapting to
the simulator's event-driven architecture and message-passing model.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

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