feat(net): track + echo movement sequence counters

Sprint 1a of the audit remediation plan.

Extracts the 4 movement sequence counters from inbound server messages
and echoes them in outbound MoveToState + AutonomousPosition instead
of hardcoded zeros:

- instanceSequence (slot 8 in CreateObject PhysicsData timestamps)
- teleportSequence (slot 4, also from PlayerTeleport 0xF751)
- serverControlSequence (slot 5)
- forcePositionSequence (slot 6, also from UpdatePosition 0xF748)

Source: holtburger player/types.rs:237-245, mutations.rs:182-706.
The server uses these to detect stale/reordered movement packets.
Previously all zeros → server couldn't distinguish epoch boundaries.

Changes:
- CreateObject.Parsed: +4 sequence fields extracted from timestamps
- UpdatePosition.Parsed: +3 sequence fields from trailing u16s
- WorldSession: tracks 4 counters, updates from CreateObject/
  UpdatePosition/PlayerTeleport for the player's own GUID
- GameWindow: passes tracked values to MoveToState.Build and
  AutonomousPosition.Build

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/AcDream.Core.Net/Messages/UpdatePosition.cs

@@ -63,7 +63,10 @@ public static class UpdatePosition
         uint Guid,
         CreateObject.ServerPosition Position,
         System.Numerics.Vector3? Velocity,
-        uint? PlacementId);
+        uint? PlacementId,
+        ushort InstanceSequence = 0,
+        ushort TeleportSequence = 0,
+        ushort ForcePositionSequence = 0);
 
     /// <summary>
     /// Parse a reassembled UpdatePosition body. <paramref name="body"/>
@@ -144,17 +147,24 @@ public static class UpdatePosition
                 pos += 4;
             }
 
-            // We deliberately skip the four u16 sequence numbers that
-            // follow; subscribers don't need them for simple rendering,
-            // and if the message is a deliberate out-of-order teleport the
-            // server always follows up with a fresher update anyway.
+            // Four u16 sequence numbers: instance, position, teleport, forcePosition.
+            ushort instSeq = 0, teleSeq = 0, forceSeq = 0;
+            if (body.Length - pos >= 8)
+            {
+                instSeq  = BinaryPrimitives.ReadUInt16LittleEndian(body.Slice(pos));
+                // pos+2 = positionSequence (not tracked by movement)
+                teleSeq  = BinaryPrimitives.ReadUInt16LittleEndian(body.Slice(pos + 4));
+                forceSeq = BinaryPrimitives.ReadUInt16LittleEndian(body.Slice(pos + 6));
+                pos += 8;
+            }
 
             var serverPos = new CreateObject.ServerPosition(
                 LandblockId: cellId,
                 PositionX: px, PositionY: py, PositionZ: pz,
                 RotationW: rw, RotationX: rx, RotationY: ry, RotationZ: rz);
 
-            return new Parsed(guid, serverPos, velocity, placementId);
+            return new Parsed(guid, serverPos, velocity, placementId,
+                instSeq, teleSeq, forceSeq);
         }
         catch
         {