feat: Adds robust speed hack detection and movement throttling (#2266)

## Summary

   Server-side movement throttle that prevents speed hacking while accurately identifying cheaters with detection of lagging connections.

   **Key features:**
   - Credit buffer (200ms) absorbs timing jitter from legitimate players
   - Movement queue handles larger bursts, draining at proper game-tick intervals
   - RTT measurement distinguishes network lag from speed hacks
   - Queue depth detection catches ACK-throttled speed hacks (going straight)

   ## How It Works

   **Throttle** (prevention): Movements arriving too early either consume credit or get queued. The queue drains at
   correct intervals, so speed hackers can't move faster regardless of what they send.

   **Detection** (identification): Combines multiple signals to identify cheaters:
   | Signal | What it catches |
   |--------|-----------------|
   | Queue depth ≥4 sustained | ACK-throttled speed hacks (client limits unacked moves to 5) |
   | Movement rate >1.05x | Direction-change speed hacks where timing is visible |
   | Stable RTT + high queue | Eliminates false positives from laggy players |

   **RTT-Aware Logic:**
   - Probes only sent to players actively moving (event-driven, not global loop)
   - Stable low-latency + problems = suspicious
   - Unstable/high-latency + problems = probably just lag, throttle handles it

   ## Configuration

   ```json
   {
     "movementThrottle.maxCredit": 200,
     "movementThrottle.softQueueLimit": 6,
     "movementThrottle.hardQueueLimit": 10,
     "movementThrottle.debugLogging": false
   }
   ```

Projects/Server/Mobiles/Mobile.cs

@@ -2522,7 +2522,7 @@ public partial class Mobile : IHued, IComparable<Mobile>, ISpawnable, IObjectPro
 
         if (ns != null)
         {
-            ns.Sequence = 0;
+            ns.ResetMovementState();
 
             if (m_Map != null)
             {
@@ -2758,7 +2758,7 @@ public partial class Mobile : IHued, IComparable<Mobile>, ISpawnable, IObjectPro
         {
             if (sendUpdate)
             {
-                ourState.Sequence = 0;
+                ourState.ResetMovementState();
                 ourState.SendMobileUpdate(this);
             }
 
@@ -4309,7 +4309,32 @@ public partial class Mobile : IHued, IComparable<Mobile>, ISpawnable, IObjectPro
 
         if (m_NetState != null)
         {
-            m_NetState._nextMovementTime += ComputeMovementSpeed(d);
+            var cost = ComputeMovementSpeed(d);
+            var now = Core.TickCount;
+            var delta = now - m_NetState._nextMovementTime;
+
+            // Cap drift to prevent banking "lateness" for speed hacking later.
+            // maxDrift should match the credit buffer so the systems are symmetric.
+            const int maxDrift = 200;
+
+            if (cost == 0)
+            {
+                // Direction-only turn: reset to now to prevent turn accumulation
+                m_NetState._nextMovementTime = now;
+            }
+            else
+            {
+                // Clamp _nextMovementTime so it's never more than maxDrift behind now.
+                // This limits how much "lateness" can be banked.
+                if (delta > maxDrift)
+                {
+                    m_NetState._nextMovementTime = now - maxDrift;
+                }
+
+                // Accumulative timing: add cost to current baseline
+                m_NetState._nextMovementTime += cost;
+            }
+
             m_NetState.SendMovementAck(m_NetState.Sequence, this);
         }
 
@@ -7249,7 +7274,7 @@ public partial class Mobile : IHued, IComparable<Mobile>, ISpawnable, IObjectPro
 
             if (isTeleport && (!m_NetState.HighSeas || !NoMoveHS))
             {
-                m_NetState.Sequence = 0;
+                m_NetState.ResetMovementState();
                 m_NetState.SendMobileUpdate(this);
             }
         }