fix: Update GPU instantiation to use GPU.GPU() in example files

[diego-betto]

Fixes "Uncaught TypeError: GPU is not a constructor" error in HTML examples.

[fuzzie360]

Closing as superseded: the root cause (GPU is not a constructor in WebGPU-capable browsers, #844) was fixed in the browser bundle itself in 2.17.1, so new GPU() in the examples is now the correct working form — switching them to the new GPU.GPU() workaround would point users at the old workaround instead. Thanks for the report that helped pin this down.