test: run tile-dependent tests on synthetic terrain instead of client files (#2725)

## Summary

About 114 tests skipped on CI because they needed the official client files (`tiledata.mul`, map and multi files). They gave CI no signal, and locally they ran against whichever client a developer had installed. The test hosts now build their own world instead, so every test runs on CI and runs the same on every machine. CI simulation: Server.Tests 837 passed, UOContent.Tests 1131 passed, **0 skipped**.

- **Generated tile data.** The fixtures write a pre-HS `tiledata.mul` from a small invented tile kit (`Server.Tests/Terrain/TestTiles`) and load it through the real `TileData.Load()`. The test hosts no longer read any client directory (`MODERNUO_CLIENT_PATH`, `MODERNUO_TEST_DATA_DIR` and `C:\Ultima Online Classic` are gone from test code). The file is written to `SyntheticData` in each test project's output, overwritten every run and removed by `dotnet clean`.
- **Injected terrain.** `TestTerrain` stamps land and statics into Felucca and Trammel, which share one terrain. Writes after startup must go in a `TestTerrain.Scope()`, which puts back every block it touched and keeps the step cache fresh.
- **Prefab scenes.** Seven named scenes (town, causeway, sewer walkway, coastline, deep sea, map-edge sea, an upstairs room with an L-shaped counter) replace the Britain coordinates the pathing, AI and fishing tests relied on. Each scene-based test asserts its scene is present first, so a missing scene fails instead of passing on flat ground. Stamping all seven takes 3-5 ms.
- **Multi footprints.** Contrived footprints for the three multi IDs content looks up (0x74, 0x7A, 0x0) are seeded through a new internal `MultiData.SetComponents`.
- **Fingerprint.** `StepCacheFile.HashTileDataFile` is extracted so a test can show that a one-flag change to the file changes the fingerprint, while runtime table mutation does not.

### Engine changes

- `TileMatrix.GetLandBlock`/`GetStaticBlock`: on a map without its files, return the block injected with `SetLandBlock`/`SetStaticBlock`, or the default when nothing was injected. Maps with files take the same path as before.
- `MultiData.SetComponents` (internal): registers a footprint without multi files.

### Test changes worth a look

- Values that were properties of real Britain terrain (probes at Z 10, a pinned plain walk mask of 0xC1) are re-pinned to the synthetic plain (Z 0, 0xFF).
- No tests were deleted. The multi walkability and boat-deck tests assert movement behaviour over a footprint, not what a real multi looks like, so they run on the contrived footprints.
- Maps 0 and 1 keep file indexes 0 and 1, and every stamp writes both, rather than sharing one file index. On a map without files the getters never consult the shared-file cache, and its patch bits would hide one facet's injection from the other.

## Test plan

- [x] `dotnet test -p:SolutionDir=... --filter "Category!=Manual"` with the client env vars pointed at an empty directory: 837 + 1131 passed, 0 skipped, 0 failed
- [x] Mutation check: removing the step-cache clear from `TestTerrain` makes the stale-cache tests fail
- [x] CI green on all platforms

Projects/UOContent.Tests/Tests/Engines/Pathing/StepCacheFileTests.cs

@@ -2,6 +2,7 @@ using System;
 using System.IO;
 using Server.Engines.Pathing.Cache;
 using Xunit;
+using static Server.Tests.Pathfinding.PathingTestSupport;
 
 namespace Server.Tests.Pathfinding;
 
@@ -195,7 +196,7 @@ public class StepCacheFileTests : IDisposable
         cache.Clear();
 
         var map = Map.Maps[1];
-        cache.TryGetMask(map, 1500, 1600, sourceZ: 10);
+        cache.TryGetMask(map, 1500, 1600, sourceZ: PlainZ);
 
         var path = Path.Combine(Path.GetTempPath(), $"step-cache-stalehash-{Guid.NewGuid():N}.swb");
         try
@@ -246,7 +247,7 @@ public class StepCacheFileTests : IDisposable
         };
         foreach (var (x, y) in coords)
         {
-            cache.TryGetMask(map, x, y, sourceZ: 10);
+            cache.TryGetMask(map, x, y, sourceZ: PlainZ);
         }
 
         var path = Path.Combine(Path.GetTempPath(), $"step-cache-lazy-{Guid.NewGuid():N}.swb");
@@ -261,7 +262,7 @@ public class StepCacheFileTests : IDisposable
             Assert.Equal(0, cache.GetStats().ResidentChunks);
 
             // Query one specific chunk: only that chunk lands in the resident set.
-            cache.TryGetMask(map, coords[0].Item1, coords[0].Item2, sourceZ: 10);
+            cache.TryGetMask(map, coords[0].Item1, coords[0].Item2, sourceZ: PlainZ);
             Assert.Equal(1, cache.GetStats().ResidentChunks);
             Assert.Equal(0L, cache.GetStats().BuildsTotal); // resolved from file, not baker
         }
@@ -291,7 +292,7 @@ public class StepCacheFileTests : IDisposable
         Assert.NotNull(map);
 
         // Build a chunk and inject a synthetic swim layer onto one cell.
-        cache.TryGetMask(map, 1500, 1600, sourceZ: 10);
+        cache.TryGetMask(map, 1500, 1600, sourceZ: PlainZ);
 
         var chunk = cache.GetResidentChunk(map.MapID, 1500 >> 4, 1600 >> 4);
         Assert.NotNull(chunk);
@@ -340,10 +341,9 @@ public class StepCacheFileTests : IDisposable
     /// to <see cref="LazyReader_DoesNotMaterializeUntilQueried"/> which proves the
     /// default lazy behavior.
     /// </summary>
-    [SkippableFact]
+    [Fact]
     public void TryOpenLazyReader_WithPreloadFlag_MaterializesAllChunksImmediately()
     {
-        TileDataRequirement.SkipIfMissing();
         var cache = StepCache.Instance;
         cache.Clear();
         cache.MissPromotionThreshold = 1;
@@ -357,7 +357,7 @@ public class StepCacheFileTests : IDisposable
         };
         foreach (var (x, y) in coords)
         {
-            cache.TryGetMask(map, x, y, sourceZ: 10);
+            cache.TryGetMask(map, x, y, sourceZ: PlainZ);
         }
 
         var path = Path.Combine(Path.GetTempPath(), $"step-cache-preload-{Guid.NewGuid():N}.swb");
@@ -374,7 +374,7 @@ public class StepCacheFileTests : IDisposable
             Assert.Equal(0L, cache.GetStats().BuildsTotal); // came from file, not baker
 
             // Subsequent query is a clean Hit, not a Miss_NotBuilt.
-            var lookup = cache.TryGetMask(map, coords[0].Item1, coords[0].Item2, sourceZ: 10);
+            var lookup = cache.TryGetMask(map, coords[0].Item1, coords[0].Item2, sourceZ: PlainZ);
             Assert.Equal(CacheHitKind.Hit, lookup.HitKind);
             Assert.Equal(coords.Length, cache.GetStats().ResidentChunks);
         }
@@ -394,10 +394,9 @@ public class StepCacheFileTests : IDisposable
     /// first pathfind through a region to use the cache rather than the slow path — the gate would
     /// otherwise defer that first touch and defeat the whole point of shipping the bake.
     /// </summary>
-    [SkippableFact]
+    [Fact]
     public void LazyReaderHit_BypassesMissTrackerOnFirstTouch()
     {
-        TileDataRequirement.SkipIfMissing();
         var cache = StepCache.Instance;
         cache.Clear();
         cache.MissPromotionThreshold = 1; // eager build for save phase
@@ -405,7 +404,7 @@ public class StepCacheFileTests : IDisposable
         var map = Map.Maps[1];
 
         // Build + save one chunk.
-        cache.TryGetMask(map, 1500, 1600, sourceZ: 10);
+        cache.TryGetMask(map, 1500, 1600, sourceZ: PlainZ);
         var path = Path.Combine(Path.GetTempPath(), $"step-cache-bypass-{Guid.NewGuid():N}.swb");
         try
         {
@@ -419,7 +418,7 @@ public class StepCacheFileTests : IDisposable
 
             // First touch must NOT return Fallthrough_NotBuilt — the lazy reader has the
             // chunk and serves it before the miss tracker is consulted.
-            var lookup = cache.TryGetMask(map, 1500, 1600, sourceZ: 10);
+            var lookup = cache.TryGetMask(map, 1500, 1600, sourceZ: PlainZ);
             Assert.True(lookup.IsHit);
             Assert.Equal(CacheHitKind.Miss_NotBuilt, lookup.HitKind);
             Assert.Equal(1, cache.GetStats().ResidentChunks);