feat: Implement Room Streaming System

- Add RoomStreamingManager to manage room loading and unloading based on player proximity.
- Create StreamingBudgetConfigSO for memory and performance budgeting of the streaming system.
- Introduce TransitionDirector to handle seamless and atmospheric fade transitions between rooms.
- Develop WorldGraph to represent room connectivity and facilitate neighbor queries and distance calculations.
- Implement RoomNode and RoomEdge classes to structure room data and connections.

Assets/_Game/Scripts/World/SpawnContext.cs

@@ -0,0 +1,24 @@
+namespace BaseGames.World
+{
+    /// <summary>
+    /// 玩家在房间激活时的出生上下文。
+    /// 由 <see cref="Streaming.RoomHandle"/> 传递给 <see cref="RoomController"/>，
+    /// 用于确定出生点位置和方向。
+    /// </summary>
+    public readonly struct SpawnContext
+    {
+        /// <summary>目标出生点 ID，对应 <see cref="PlayerSpawnPoint.TransitionId"/>。null 时使用默认出生点。</summary>
+        public readonly string EntryTransitionId;
+
+        /// <summary>true = 死亡复活流程，不播放入场动画。</summary>
+        public readonly bool IsRespawn;
+
+        public SpawnContext(string entryTransitionId, bool isRespawn = false)
+        {
+            EntryTransitionId = entryTransitionId;
+            IsRespawn         = isRespawn;
+        }
+
+        public static readonly SpawnContext Default = new SpawnContext(null, false);
+    }
+}