feat: implement raft log replication and apply

src/NATS.Server/Raft/RaftLog.cs

@@ -0,0 +1,25 @@
+namespace NATS.Server.Raft;
+
+public sealed class RaftLog
+{
+    private readonly List<RaftLogEntry> _entries = [];
+
+    public IReadOnlyList<RaftLogEntry> Entries => _entries;
+
+    public RaftLogEntry Append(int term, string command)
+    {
+        var entry = new RaftLogEntry(_entries.Count + 1, term, command);
+        _entries.Add(entry);
+        return entry;
+    }
+
+    public void AppendReplicated(RaftLogEntry entry)
+    {
+        if (_entries.Any(e => e.Index == entry.Index))
+            return;
+
+        _entries.Add(entry);
+    }
+}
+
+public sealed record RaftLogEntry(long Index, int Term, string Command);