feat(gpu): add WebGPU compute profile

[replghost]

Summary

• add expanded webgpu profile alongside raster-only webgpu-raster
• add compute pipeline/pass/dispatch GPU wire commands and writable storage buffer bindings
• implement native wgpu and browser WebGPU compute execution, validation, docs, tests, and rebuilt browser assets

Verification

• cargo +nightly fmt
• cargo test -p pvm-gpu-wire
• cargo test -p pvm-runtime --all-features
• cargo test -p pvm-runtime-assets
• npm test --workspace @parity/pvm-browser-runtime
• node scripts/verify-browser-assets.mjs