Curated NotifyLogin data, cleaned up handlers and rearranged code

AscNet.GameServer/Handlers/HeartbeatModule.cs

@@ -0,0 +1,19 @@
+using AscNet.Common.MsgPack;
+
+namespace AscNet.GameServer.Handlers
+{
+    internal class HeartbeatModule
+    {
+        [RequestPacketHandler("HeartbeatRequest")]
+        public static void HeartbeatRequestHandler(Session session, Packet.Request packet)
+        {
+            HeartbeatResponse heartbeatResponse = new()
+            {
+                UtcServerTime = DateTimeOffset.UtcNow.ToUnixTimeSeconds()
+            };
+            session.SendResponse(heartbeatResponse, packet.Id);
+        }
+
+        // TODO: Pong?
+    }
+}