feat: add streaming primitives (IChunkRenderer, IJobExecutor, NeighborSnapshots, ChunkJob)

World/Streaming/ChunkJob.cs

@@ -0,0 +1,21 @@
+using OpenTK.Mathematics;
+using VoxelEngine.World.Chunk;
+
+namespace VoxelEngine.World.Streaming;
+
+// Job dispatched to an IJobExecutor. For a fresh load, ExistingChunk is null
+// and the worker generates + applies diff + meshes. For a remesh-only job,
+// ExistingChunk holds the chunk and the worker only meshes (no generation).
+internal sealed record ChunkJob(
+    Vector3i Pos,
+    Chunk.Chunk? ExistingChunk,
+    NeighborSnapshots Neighbors,
+    IReadOnlyDictionary<int, ushort>? Diff);
+
+// Posted by the worker back to the main thread via a ConcurrentQueue.
+internal sealed record ChunkJobResult(
+    Vector3i Pos,
+    Chunk.Chunk? Chunk,
+    float[]? Mesh,
+    Exception? Error,
+    bool IsRemeshOnly);