feat: Add CanSpawnMobile overload with props Z-range support. (#2293)

### Summary

- Adds CanSpawnMobile(x, y, minZ, maxZ, canSwim, cantWalk, out spawnZ) overload for finding spawn surfaces within a Z range
- Adds CanSpawnItem(x, y, minZ, maxZ, out spawnZ) for item spawning with Surface+Impassable support (tables, furniture)
- Uses bitmask optimization inspired by Item.DropToWorld's m_OpenSlots pattern for O(1) surface/blocker checks
- HomeRange spawners now use surface detection to set proper Z bounds

### Key Changes

Map.cs:
- CanSpawnMobile with Z-range finds lowest valid surface for mobiles
- CanSpawnItem with Z-range finds lowest valid surface for items (including tables)
- CanFitItem for point-check item placement on Surface+Impassable tiles
- Bitmask approach eliminates nested loops and stackalloc arrays

Spawners:
- Simplified GetSpawnPosition using new Z-range methods
- HomeRange setter detects surface below spawner for proper Z bounds
- Consistent handling for mobiles and items

### Bug Fixes

- Water tiles (Impassable | Wet) no longer block swimming mobs
- Items can now spawn on tables/furniture (Surface+Impassable)

### Test Plan

- Run dotnet test - 631 tests pass
- Manual testing: multi-story spawning, water mobs, item spawning on tables
- Verify HomeRange spawner movement shifts bounds correctly

Projects/Server.Tests/Fixtures/ServerFixture.cs

@@ -1,38 +1,43 @@
 using System;
-using System.Reflection;
 using Xunit;
 
 namespace Server.Tests;
 
+/// <summary>
+/// Fixture for all server tests. Attempts to load TileData from client files if available.
+/// Configure client path via MODERNUO_CLIENT_PATH environment variable or place files at C:\Ultima Online Classic.
+/// </summary>
 [CollectionDefinition("Sequential Server Tests", DisableParallelization = true)]
 public class ServerFixture : ICollectionFixture<ServerFixture>, IDisposable
 {
+    /// <summary>
+    /// True if TileData was successfully loaded from client files.
+    /// </summary>
+    public static bool TileDataLoaded => TestServerInitializer.TileDataLoaded;
+
+    /// <summary>
+    /// A tile ID known to have the Surface flag. 0 if not found.
+    /// </summary>
+    public static ushort SurfaceTileId => TestServerInitializer.SurfaceTileId;
+
+    /// <summary>
+    /// A tile ID known to have the Impassable flag. 0 if not found.
+    /// </summary>
+    public static ushort ImpassableTileId => TestServerInitializer.ImpassableTileId;
+
+    /// <summary>
+    /// A tile ID known to have the Wet flag (water). 0 if not found.
+    /// </summary>
+    public static ushort WetTileId => TestServerInitializer.WetTileId;
+
+    /// <summary>
+    /// A tile ID known to have both Surface and Impassable flags (tables, furniture). 0 if not found.
+    /// </summary>
+    public static ushort SurfaceImpassableTileId => TestServerInitializer.SurfaceImpassableTileId;
+
     public ServerFixture()
     {
-        Core.ApplicationAssembly = Assembly.GetExecutingAssembly(); // Server.Tests.dll
-
-        // Load Configurations
-        ServerConfiguration.Load(true);
-
-        // Load an empty assembly list into the resolver
-        ServerConfiguration.AssemblyDirectories.Add(Core.BaseDirectory);
-        AssemblyHandler.LoadAssemblies(["Server.dll"]);
-
-        Core.LoopContext = new EventLoopContext();
-        Core.Expansion = Expansion.EJ;
-
-        // Configure / Initialize
-        TestMapDefinitions.ConfigureTestMapDefinitions();
-
-        // Configure the world
-        World.Configure();
-
-        Timer.Init(0);
-
-        // Load the world
-        World.Load();
-
-        World.ExitSerializationThreads();
+        TestServerInitializer.Initialize(loadTileData: true);
     }
 
     public void Dispose()