Add raft-core TypeScript implementation

[maboke123]

Adding @maboke123/raft-core, a TypeScript implementation of Raft with:

• Leader election with pre-vote
• Log replication
• Snapshots
• Joint consensus cluster membership changes (addServer, removeServer, promoteServer)
• Pluggable storage (InMemoryNodeStorage, DiskNodeStorage) and transport (GrpcTransport)
• Full event stream for observability
• Published on npm as @maboke123/raft-core and @maboke123/raft-grpc

Also includes a React devtools visualizer for observing live cluster state, elections, and message flow.