Performance Optimization — Paid By Blood Steam update #723670

The performance of Level 3 has been optimized. 1. Added a simple level loading mechanism. Now, the corresponding buildings will only be loaded when they are close by. Since it is not an asynchronous loading, there may be a short period of lag during loading. 2. Reduced the model quality of Level 3. Significantly reduced the number of faces of some high-precision models. 3. The trees in Level 3 now sway with the wind. 4. Removed the loading buffer interface as it causes abnormal loading behavior. In case of any bugs, you can switch to the "release_windows" branch. This is an older version that is guaranteed to work properly (on my computer).