feat: Add support for asynchronous pipeline creation

[reczkok]

I feel like an API like that would be nice to have and citing MDN, creating pipelines asynchronously "is generally preferable"

We currently create all pipelines and resources lazily synchronously but maybe the future is asynchronous? I feel like that could enable us to distribute the work nicely (for example when creating multiple pipelines one can begin asynchronously being created by WebGPU API while we begin resolving the next)

[iwoplaza]

I really like this idea. I'd keep the lazy nature of our pipelines, as that makes it very handling in environments like React where resources can be created and destroyed many times before they're even used.

const root = await tgpu.init();
const pipeline = root.createRenderPipeline({
  vertex: ({ $vertexIndex: vid }) => {
    'use gpu';
    return {
      $position: d.vec4f(pos.$[vid], 0, 1),
      uv: uv.$[vid],
    };
  },
  fragment: ({ uv }) => {
    'use gpu';
    return getGradientColor((uv.x + uv.y) / 2);
  },
});

await pipeline.initAsync();

initAsync would return a resolved promise if the pipeline has been created, a pending promise if initialization has already been requested, and if it hasn't, it would trigger the pipeline creation using .create*PipelineAsync instead of the sync variant. If any other APIs or the user tried to root.unwrap the pipeline during this process, we would throw.

We could also create the sync variant as well pipeline.initSync(), to be used instead of root.unwrap for triggering pipeline creation.

[reczkok]

Remember to update the skill once done, thx