feat: Adds grid support for the DynamicGump system (#2306)

### Summary 

- Adds a new grid layout system for DynamicGump with zero heap allocations
 - Migrates SpawnerControllerGump from legacy GumpGrid to DynamicGump
 - Migrates CommandListGump from BaseGridGump to DynamicGump
 - Removes legacy GumpGrid (no longer needed)

 ### New Grid Layout Components

 | Component | Purpose |
 |-----------|---------|
 | `GridCell` | Value type for cell bounds (x, y, width, height) |
 | `GridSizeSpec` | Parses CSS-like sizing specs ("10*", "*", "100") |
 | `GridCalculator` | Computes track positions using stackalloc |
 | `ListViewLayout` | Pagination + column layout for list views |
 | `GridBuilderExtensions` | Extension methods accepting `GridCell` |
 | `GridEntryStyle` | Styling properties for BaseGridGump migration |
 | `GridEntryExtensions` | Entry methods matching BaseGridGump patterns |

 ### Memory Impact

 | Component | Legacy | New |
 |-----------|--------|-----|
 | Grid storage | ~200 bytes heap | 0 bytes (stackalloc) |
 | Column/Row lists | ~400 bytes heap | ~128 bytes stack |
 | ListView | ~300 bytes heap | ~64 bytes stack |
 | **Total per render** | **~900 bytes heap** | **0 bytes heap** |

 ### Test plan

 - [x] All 21 gump tests pass
 - [x] Build succeeds with no warnings
 - [ ] In-game verification of SpawnerControllerGump
 - [ ] In-game verification of CommandListGump (HelpInfo command)

Projects/UOContent/Gumps/Base/GridLayout/GridCell.cs

@@ -0,0 +1,114 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2025 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: GridCell.cs                                                     *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System.Runtime.CompilerServices;
+
+namespace Server.Gumps;
+
+/// <summary>
+/// Represents a pre-calculated cell position within a grid layout.
+/// This is a value type with zero heap allocations.
+/// </summary>
+public ref struct GridCell
+{
+    public readonly int X;
+    public readonly int Y;
+    public readonly int Width;
+    public readonly int Height;
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public GridCell(int x, int y, int width, int height)
+    {
+        X = x;
+        Y = y;
+        Width = width;
+        Height = height;
+    }
+
+    /// <summary>
+    /// Gets the right edge X coordinate (X + Width).
+    /// </summary>
+    public int Right
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get => X + Width;
+    }
+
+    /// <summary>
+    /// Gets the bottom edge Y coordinate (Y + Height).
+    /// </summary>
+    public int Bottom
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get => Y + Height;
+    }
+
+    /// <summary>
+    /// Gets the horizontal center X coordinate.
+    /// </summary>
+    public int CenterX
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get => X + Width / 2;
+    }
+
+    /// <summary>
+    /// Gets the vertical center Y coordinate.
+    /// </summary>
+    public int CenterY
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get => Y + Height / 2;
+    }
+
+    /// <summary>
+    /// Creates a new cell with uniform margin inset on all sides.
+    /// </summary>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public GridCell Inset(int margin) =>
+        new(X + margin, Y + margin, Width - margin * 2, Height - margin * 2);
+
+    /// <summary>
+    /// Creates a new cell with separate horizontal and vertical margins.
+    /// </summary>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public GridCell Inset(int horizontal, int vertical) =>
+        new(X + horizontal, Y + vertical, Width - horizontal * 2, Height - vertical * 2);
+
+    /// <summary>
+    /// Creates a new cell with individual margins for each side.
+    /// </summary>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public GridCell Inset(int left, int top, int right, int bottom) =>
+        new(X + left, Y + top, Width - left - right, Height - top - bottom);
+
+    /// <summary>
+    /// Creates a new cell with an offset applied to the position.
+    /// </summary>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public GridCell Offset(int offsetX, int offsetY) => new(X + offsetX, Y + offsetY, Width, Height);
+
+    /// <summary>
+    /// Creates a new cell with a different width.
+    /// </summary>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public GridCell WithWidth(int width) => new(X, Y, width, Height);
+
+    /// <summary>
+    /// Creates a new cell with a different height.
+    /// </summary>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public GridCell WithHeight(int height) => new(X, Y, Width, height);
+}