feat(core): add WorldView with 3x3 neighbor landblock computation

tests/AcDream.Core.Tests/World/WorldViewTests.cs

@@ -0,0 +1,46 @@
+// tests/AcDream.Core.Tests/World/WorldViewTests.cs
+using AcDream.Core.World;
+
+namespace AcDream.Core.Tests.World;
+
+public class WorldViewTests
+{
+    [Fact]
+    public void NeighborIds_Center_Returns9Ids()
+    {
+        var ids = WorldView.NeighborLandblockIds(0xA9B4FFFFu).ToList();
+
+        Assert.Equal(9, ids.Count);
+        Assert.Contains(0xA9B4FFFFu, ids);  // center
+        Assert.Contains(0xA8B3FFFFu, ids);  // NW
+        Assert.Contains(0xAAB5FFFFu, ids);  // SE
+    }
+
+    [Fact]
+    public void NeighborIds_LowerEdge_ClampsUnderflow()
+    {
+        // Landblock 0x0000FFFF — no west or south neighbors.
+        var ids = WorldView.NeighborLandblockIds(0x0000FFFFu).ToList();
+
+        // 4 neighbors should exist: center + E + N + NE
+        Assert.Equal(4, ids.Count);
+        Assert.Contains(0x0000FFFFu, ids);
+        Assert.Contains(0x0100FFFFu, ids);
+        Assert.Contains(0x0001FFFFu, ids);
+        Assert.Contains(0x0101FFFFu, ids);
+    }
+
+    [Fact]
+    public void NeighborIds_UpperEdge_ClampsOverflow()
+    {
+        // Landblock 0xFFFFFFFF — no east or north neighbors.
+        var ids = WorldView.NeighborLandblockIds(0xFFFFFFFFu).ToList();
+
+        // 4 neighbors: center + W + S + SW
+        Assert.Equal(4, ids.Count);
+        Assert.Contains(0xFFFFFFFFu, ids);
+        Assert.Contains(0xFEFFFFFFu, ids);
+        Assert.Contains(0xFFFEFFFFu, ids);
+        Assert.Contains(0xFEFEFFFFu, ids);
+    }
+}