Core/Units: moved cyclic spline synchronization mechanic heartbeat handling

Port From (https://github.com/TrinityCore/TrinityCore/commit/c2fedbb6cc89510002e9f56751e7f8427e306487)

Source/Game/Entities/Unit/Unit.Fields.cs

@@ -27,7 +27,6 @@ namespace Game.Entities
         public MoveSpline MoveSpline { get; set; }
         MotionMaster i_motionMaster;
         public uint m_movementCounter;       //< Incrementing counter used in movement packets
-        TimeTracker splineSyncTimer;
         MovementForces _movementForces;
         PositionUpdateInfo _positionUpdateInfo;
         protected Unit m_unitMovedByMe;    // only ever set for players, and only for direct client control

Source/Game/Entities/Unit/Unit.Movement.cs

@@ -1809,20 +1809,6 @@ namespace Game.Entities
             MoveSpline.UpdateState((int)diff);
             bool arrived = MoveSpline.Finalized();
 
-            if (MoveSpline.IsCyclic())
-            {
-                splineSyncTimer.Update(diff);
-                if (splineSyncTimer.Passed())
-                {
-                    splineSyncTimer.Reset(5000); // Retail value, do not change
-
-                    FlightSplineSync flightSplineSync = new();
-                    flightSplineSync.Guid = GetGUID();
-                    flightSplineSync.SplineDist = (float)MoveSpline.TimePassed() / MoveSpline.Duration();
-                    SendMessageToSet(flightSplineSync, true);
-                }
-            }
-
             if (arrived)
             {
                 DisableSpline();
@@ -1860,6 +1846,17 @@ namespace Game.Entities
             UpdatePosition(loc.X, loc.Y, loc.Z, loc.W);
         }
 
+        void SendFlightSplineSyncUpdate()
+        {
+            if (!MoveSpline.IsCyclic() || MoveSpline.Finalized())
+                return;
+
+            FlightSplineSync flightSplineSync = new();
+            flightSplineSync.Guid = GetGUID();
+            flightSplineSync.SplineDist = (float)MoveSpline.TimePassed() / MoveSpline.Duration();
+            SendMessageToSet(flightSplineSync, true);
+        }
+
         void InterruptMovementBasedAuras()
         {
             // TODO: Check if orientation transport offset changed instead of only global orientation

Source/Game/Entities/Unit/Unit.cs

@@ -70,8 +70,6 @@ namespace Game.Entities
 
             m_serverSideVisibility.SetValue(ServerSideVisibilityType.Ghost, GhostVisibilityType.Alive);
 
-            splineSyncTimer = new TimeTracker();
-
             m_unitData = new UnitData();
         }
 
@@ -2557,6 +2555,14 @@ namespace Game.Entities
             return m_deathState;
         }
 
+        public override void Heartbeat()
+        {
+            base.Heartbeat();
+
+            // SMSG_FLIGHT_SPLINE_SYNC for cyclic splines
+            SendFlightSplineSyncUpdate();
+        }
+
         public bool HaveOffhandWeapon()
         {
             if (IsTypeId(TypeId.Player))