The vulkan backend was implemented with async in mind, however the one place
where Blender uses for async was implemented blocking. This PR splits the
readback into flushing the command and waiting for readback.
**Performance**
Improvement of animation playback performance of shader balls.blend is around 10%.
Shader balls.blend frame: 1-100, 10 x animation playback
| Branch | Total time | Average time |
| -------------------- | ---------- | ------------ |
| blender-v4.4-release | 26851 ms | 2685 ms |
| This PR | 23675 ms | 2367 ms |
Pull Request: https://projects.blender.org/blender/blender/pulls/134227
0faba244a5