fix: Fixes tick count wrap-around in movement throttle, and eliminates more allocations in NetState (#2603)

## Summary

Removes the per-tick allocation in the movement throttle, fixes tick-count wrap-around bugs in the throttle and RTT probe state, and trims per-connection allocations and dead fields in `NetState`.

## Movement throttle

- **No more per-tick `List<NetState>` snapshot.** `ProcessAllQueues()` iterates the `HashSet` directly and removes drained or disconnected states in place. `HashSet<T>.Remove` does not invalidate enumerators on .NET Core 3.0+ (verified on 10.0.11); only inserting a *new* member does, and the only `Add` is in the packet handler, which never nests with `Slice()`. The eager `Remove` calls in `RejectAndReset`, `ClearQueue`, and `ProcessMovementQueue` are gone; membership is reconciled once per tick from `_hasQueuedMovements`.
- **Debug logging** is now gated solely by the per-connection `NetState.MovementLogging` flag. The global `movementThrottle.debugLogging` setting is removed.
- **New settings**: `movementThrottle.maxRttBonus`, `movementThrottle.maxChainGap`, and `movementThrottle.speedHackNotificationCooldown` were fields with no config binding.

## Tick-count wrap-around

All comparisons are now in subtraction form and no tick field uses zero as a sentinel:

- `now < _nextMovementTime` in the queue drain loop → `now - _nextMovementTime < 0`.
- `_lastMovementRecordTime > 0`, `_lastSpeedHackNotification`, `_rttProbeTime > 0`, and `_nextRttProbe == 0` sentinels replaced with `_hasMovementRecord`, `_speedHackNotified`, `_rttProbePending`, and a seeded `_nextRttProbe`.
- `_lastQueueDepthCheck` and `_movementWindowStart` are seeded from `Core.TickCount` at construction and on reset instead of zero.

User-visible effects of the old code: on hosts with pass-through counters (GCP) movement history never recorded and speed hack detection was silently off; on every host, staff speed hack notifications were suppressed until `Core.TickCount` exceeded the five-minute cooldown.

## NetState

- `Instances` returns `HashSet<NetState>` again so engine-internal `foreach` uses the struct enumerator instead of boxing through `IReadOnlySet<T>`.
- Removed `_sustainedQueueDepth` (declared and zeroed since #2266, never read), `_lastRtt` (now derived as `LastRtt` from the newest history slot), and `_rttProbeTimestampHiRes` (only fed one debug log line). 20 bytes per connection.
- `HuePickers`, `Menus`, and `Trades` are lazily created instead of allocating three lists per connection, including every login-server connection that dies on shard select. `Trades` is released when it empties. All helpers and the `HuePickerResponse` / `MenuResponse` handlers are null-tolerant; the trade cancel loops keep their `i < Count` guards because `SecureTrade.Cancel()` runs virtual item hooks that can re-enter the same list.

## Testing

- `dotnet build -c Release` clean.
- All MovementThrottle tests pass (27), plus the Trade / Menu / HuePicker / NetState tests (32).

Projects/Server/Network/NetState/NetState.cs

@@ -44,7 +44,7 @@ public partial class NetState : IComparable<NetState>, IValueLinkListNode<NetSta
 
     private static readonly Queue<NetState> _connectingQueue = new(2048);
     private static readonly HashSet<NetState> _instances = new(2048);
-    public static IReadOnlySet<NetState> Instances => _instances;
+    public static HashSet<NetState> Instances => _instances;
 
     private readonly string _toString;
     private ClientVersion _version;
@@ -109,9 +109,6 @@ public partial class NetState : IComparable<NetState>, IValueLinkListNode<NetSta
         Address = address;
 
         Seeded = false;
-        HuePickers = [];
-        Menus = [];
-        Trades = [];
         NextActivityCheck = Core.TickCount + 30000;
         ConnectedOn = Core.Now;
         _toString = address?.ToString() ?? "(error)";
@@ -166,7 +163,7 @@ public partial class NetState : IComparable<NetState>, IValueLinkListNode<NetSta
 
     public bool BlockAllPackets { get; set; }
 
-    public List<SecureTrade> Trades { get; }
+    public List<SecureTrade> Trades { get; private set; }
 
     public bool Seeded { get; set; }
 
@@ -260,8 +257,18 @@ public partial class NetState : IComparable<NetState>, IValueLinkListNode<NetSta
 
     public void ValidateAllTrades()
     {
+        if (Trades == null)
+        {
+            return;
+        }
+
         for (var i = Trades.Count - 1; i >= 0; --i)
         {
+            if (Trades == null)
+            {
+                break;
+            }
+
             if (i >= Trades.Count)
             {
                 continue;
@@ -280,8 +287,18 @@ public partial class NetState : IComparable<NetState>, IValueLinkListNode<NetSta
 
     public void CancelAllTrades()
     {
+        if (Trades == null)
+        {
+            return;
+        }
+
         for (var i = Trades.Count - 1; i >= 0; --i)
         {
+            if (Trades != null)
+            {
+                break;
+            }
+
             if (i < Trades.Count)
             {
                 Trades[i].Cancel();
@@ -291,11 +308,21 @@ public partial class NetState : IComparable<NetState>, IValueLinkListNode<NetSta
 
     public void RemoveTrade(SecureTrade trade)
     {
-        Trades.Remove(trade);
+        Trades?.Remove(trade);
+
+        if (Trades?.Count == 0)
+        {
+            Trades = null;
+        }
     }
 
     public SecureTrade FindTrade(Mobile m)
     {
+        if (Trades == null)
+        {
+            return null;
+        }
+
         for (var i = 0; i < Trades.Count; ++i)
         {
             var trade = Trades[i];
@@ -311,6 +338,11 @@ public partial class NetState : IComparable<NetState>, IValueLinkListNode<NetSta
 
     public SecureTradeContainer FindTradeContainer(Mobile m)
     {
+        if (Trades == null)
+        {
+            return null;
+        }
+
         for (var i = 0; i < Trades.Count; ++i)
         {
             var trade = Trades[i];
@@ -336,7 +368,11 @@ public partial class NetState : IComparable<NetState>, IValueLinkListNode<NetSta
     {
         var newTrade = new SecureTrade(Mobile, state.Mobile);
 
+        Trades ??= [];
+
         Trades.Add(newTrade);
+
+        state.Trades ??= [];
         state.Trades.Add(newTrade);
 
         return newTrade.From.Container;
@@ -1176,8 +1212,16 @@ public partial class NetState : IComparable<NetState>, IValueLinkListNode<NetSta
 
         var a = Account;
 
-        Menus.Clear();
-        HuePickers.Clear();
+        Menus?.Clear();
+        Menus = null;
+
+        HuePickers?.Clear();
+        HuePickers = null;
+
+        // Just in case, but should already be nulled when Mobile.NetState is set to null and CancelAllTrades is called.
+        Trades?.Clear();
+        Trades = null;
+
         Account = null;
         ServerInfo = null;
         CityInfo = null;