feat(vis-core): WebGPU Buffer Memory Management

[Jarbuckle]

feat(vis-core): WebGPU Buffer Memory Management

What

Introduces the memory module of the WebGPU rendering subsystem: the BufferManager interface and BatchPoolBufferManager, a pooling implementation that suballocates from size-bucketed slabs so many small resources share a few large GPUBuffers.

Stacked on the WebGPU test setup; resources, renderer, and the demo page follow.

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