Add manual `wgpu` API

This will require some changes to how wgpu-native works, namely we'll definitely want to be able to return Bevy's instance rather than requiring users to create a new instance themselves. libprocessing will need to ship with a defined version of wgpu-native that users will be expected to interact with if they want to share wgpu handles between libprocessing and their custom WebGPU code. There's a ton of trickiness here and this will likely be a pretty difficult task.

未指定檔案、測試或進入點。先追蹤 libprocessing 目前如何建立並公開其 Bevy 和 wgpu-native 執行個體，然後檢視預期的 wgpu-native 版本以及 handle 共用邊界。完成的標準是：在不要求使用者建立個別執行個體的情況下，手動 wgpu API 和執行個體共用行為已定義並實作。